CHEMISTRY  OF  PULP 
AND    PAPER    MAKING 


BY 

EDWIN  S.UTERMEISTER,  S.  B. 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN  &  HALL,   LIMITED 
IQ20 


COPYRIGHT,  1920 

BY 
EDWIN  SUTERMEISTER 


Manufactured  in  the  U.S.A. 


PREFACE 

The  preparation  of  this  book  was  undertaken  because  it  was 
felt  that  there  was  need  of  a  work  dealing  primarily  with  the 
chemical  aspects  of  the  pulp  and  paper  industry  and  embodying 
under  one  cover  the  results  of  recent  investigations  along  this 
line.  The  endeavor  has  been  to  include  all  details  which  the 
chemist  should  have  to  enable  him  to  grasp  the  methods  of 
manufacture,  but  it  is  not  intended  to  be  a  treatise  on  paper 
making  in  all  its  mechanical  phases,  and  in  fact  the  mechanical 
features  of  the  industry  are  discussed  only  in  so  far  as  they  are 
necessary  for  a  satisfactory  understanding  of  the  chemistry 
involved.  It  has  been  written  chiefly  with  the  idea  of  helping 
the  young  technical  man,  whether  chemist  or  chemical  engineer, 
and  it  has  therefore  been  assumed  that  the  reader  has  a  fair 
knowledge  of  the  elements  of  chemistry.  At  the  same  time  it 
has  been  attempted  to  write  as  simply  and  plainly  as  possible 
and  it  is  believed  that  any  one  connected  with  the  pulp  and 
paper  industry  will  find  it  helpful  and  suggestive. 

The  subject  matter  has  been  collected  from  personal  notes 
and  experiences  during  the  author's  twenty  years'  service  as 
chemist  in  the  industry,  as  well  as  from  a  careful  review  of  the 
literature  relating  to  the  subject.  The  latter  is  often  contra- 
dictory in  the  extreme  and  in  certain  cases  it  has  proved  almost 
impossible  to  reconcile  conflicting  statements.  In  such  cases 
both  sides  of  the  argument  have  been  presented  as  fairly  as 
possible.  It  is  peculiar  to  the  industry  that  there  are  usually 
a  large  number  of  variable  factors  which  influence  any  one 
operation,  and  since  it  is  practically  impossible  to  control  all 
of  these  variables  it  necessarily  follows  that  results  in  different 
mills  will  not  be  in  harmony.  For  this  reason  it  is  expected 

that  the  observant  reader  will  find  statements  to  which  he 

iii 


IV  PREFACE 

will  take  exceptions,  but  such  differences  of  opinion  are  often 
desirable  since  they  indicate  lines  of  investigation  which  will 
lead  to  a  better  understanding  of  many  things  which  are  at 
present  obscure. 

Regarding  the  methods  of  analysis  and  testing  which  are 
given  it  may  be  said  that  the  attempt  has  been  made  to  include 
all  which  are  necessary  for  routine  work  in  controlling  opera- 
tions. There  are  many  occasional  analyses  which  it  is  necessary 
to  make  during  special  investigations,  but  it  is  impractical  to 
include  all  of  these  and  for  such  methods  reference  must  be 
made  to  the  numerous  standard  text-books  of  analytical 
procedure. 

Acknowledgment  is  made  of  the  assistance  of  Mr.  J.  L.  Merrill 
on  the  subject  of  "Straw"  and  also  of  that  of  my  associates  at 
the  mills  of  S.  D.  Warren  Company,  whose  encouragement  has 
helped  to  overcome  many  difficulties. 

I  am  also  indebted  to  the  publishers  of  Van  Nostrand's  Chem- 
ical Annual  for  a  number  of  the  tables  which  will  be  found  in 
the  appendix. 


CONTENTS 

i 

CHAPTER  I  PAGE 

CELLULOSE ! 

Physiological  and  Physical.  Composition  and  Constitution.  Cellulose 
and  Water.  Solvents.  Cellulose  and  Salts.  Decomposition  by  Acids, 
Alkalis,  Oxidants,  Ferments  and  Heat.  Compounds,  Nitrates,  Gun- 
Cotton,  Nitrites,  Acetates,  Sulphuric  Esters.  Mixed  Esters,  Benzoates, 
Formates,  Alkali-Cellulose.  Sulpho-Carbonates.  Groups  of  Celluloses. 
Compound  Celluloses.  Methods  of  Determination. 

CHAPTER  II 

FIBROUS  RAW  MATERIALS t . . .      34 

The  Vegetable  Cell.  Seed  Hairs.  Bast  Fibres.  Fibres  from  Whole 
Stems.  Woods.  Length  of  Fibres.  Densities  and  Composition  of 
Woods.  Bark  and  Knots.  Decay.  Woods  used  in  Pulp  Making. 
Bulk  of  Raw  Materials. 

CHAPTER  III 

RAGS,  ESPARTO,  STRAW,  BAMBOO 68 

Grades  of  Rags.  Dusting.  Boiling.  Boilers.  Losses.  Esparto.  Clean- 
ing. Boilers.  Cooking.  Bleaching.  Alkali  Recovery.  Straw.  Com- 
position. Cooking  with  Lime.  Soda  Cooks.  Bamboo.  Sources. 
Analyses.  Cooking.  Fibres  from  Old  Papers. 

CHAPTER  IV 
THE  SODA  PROCESS 93 

Raw  Materials.  Digesters.  Causticizing.  Lime  Mud.  Cooking  Liquor. 
Boiling.  Effect  of  varying  Steam  Pressure,  Strength  of  Cooking  Liquor, 
Alkali  Added,  and  Time  of  Cooking,  Speed  of  Reaction.  Soda 
Consumption.  Yields.  Modified  Processes.  Relief  gases.  Blow 
Tanks.  Wash  Pits  and  Washing.  Black  Liquor.  Recovery  of  Soda. 
Evaporators.  Incinerators.  Black  Ash  Waste.  Losses.  Tests  and 
Analyses. 

CHAPTER  V 

THE  SULPHATE  PROCESS 141 

Kraft  Fibre.  Cooking.  Liquor  Composition.  Yields.  Odors.  Blow-off 
Gases.  Black  Liquor.  Soda  Recovery.  Smelting.  Composition  of 
Melt.  Tests  and  Analyses. 


vi  CONTENTS 

CHAPTER  VI  PAGE 

THE  SULPHITE  PROCESS 156 

Theory.  Wood  and  its  Preparation.  Liquor  Making.  Sulphur  Burning. 
Burning  Pyrites.  Absorption  Apparatus.  Quality  of  Lime  Desired. 
Losses.  Composition  of  Acid.  Storage.  Digesters  and  Linings.  Boiling. 
Mitscherlich  Process.  Ritter-Kellner  Process.  Records  and  Charts. 
Relieving  Gas.  Following  the  Progress  of  a  Cook.  Recovery  of  Gas. 
Blowing  the  Charge.  Washing.  Composition  of  Products.  Modified 
Processes.  By-products  and  Waste  Liquor.  Tests  and  Analyses. 

CHAPTER  VII 

GROUND  WOOD  OR  MECHANICAL  PULP 212 

Outline  of  Process.  Grinders.  Factors  Influencing  Results.  Steamed 
Wood.  Woods  Available.  Enge  Process.  Examination  of  Product. 
Bleaching. 

CHAPTER  VIII 

BLEACHING 225 

Properties  of  Chlorine.  Gas  Bleaching.  Hypochlorites.  Bleaching 
Powder  and  its  Solutions.  Electrolytic  Bleach.  Principles  of  Bleaching. 
Weight  of  Fibre  Lost  on  Bleaching.  Change  in  Color  on  Bleaching. 
Use  of  Backwater.  Bleaching  Systems.  Ground  Wood.  Antichlors. 
Washing  Bleached  Pulp.  Permanganate  Bleaching.  Effect  on  Strength 
and  Chemical  Properties  of  Stock.  Testing  Bleaching  Powder. 

CHAPTER  IX 
SIZING 257 

Necessity  for  Sizing.  Surface  Sizing..  Gelatine  and  its  Testing.  Starch. 
Rosin.  Source  and  Properties.  Size  Making.  Reactions  of  Sizing. 
Rosin  Required.  Defects  in  Rosin  Sizing.  Testing  Rosin  and  Sizes. 
Alum.  Preparation.  Composition.  Testing.  Casein  Sizing.  Glue 
Sizing.  Rubber  Resins.  Mitscherlich  Process. 

CHAPTER  X 

LOADING  AND  FILLING  MATERIALS 290 

Reason  for  Using.  Effect  on  Sizing.  Qualities  Desired.  Retention. 
Clay.  Gypsum.  Pearl  Hardening.  Precipitated  Chalk.  Talc.  Asbes- 
tine. Heavy  Spar.  Testing. 

CHAPTER  XI 

COLORING 306 

Importance.  Pigments.  Natural  Mineral  Colors.  Artificial  Mineral 
Colors.  Natural  Organic  Colors.  Artificial  Organic  Colors.  Union  of 
Dye  and  Filler.  Effect  of  Water  on  Dyes.  Direct  Cotton  Colors.  Basic 
Colors.  Eosines  and  Rhodamines.  Acid  Colors.  Organic  Pigments. 
Calender  Staining.  Testing  Colors. 


CONTENTS  Vli 

CHAPTER  XII  PAGE 

COATED  PAPERS 325 

Advantages  and  Disadvantages.  Body  Stock.  Applying  the  Coating. 
Influence  of  Adhesives.  Finishing  Coated  Papers.  Glue  Requirements 
for  Coating.  Casein,  Source  and  Composition.  Solvents.  Preservation 
of  Solutions.  Testing.  Albumen.  Starch.  Modified  Starches.  Clay. 
Blanc  Fixe  and  Barytes.  Satin  White.  Accessories. 

CHAPTER  XIII 

WATER 351 

Importance  in  Paper  Making.  Classification  and  Sources.  Color. 
Boiler  Scale  Formation.  Water  Softening.  Filtration.  Methods  of 
Sampling  and  Analysis. 

CHAPTER  XIV 
TESTING  WOOD  PULPS 368 

Moisture  in  Baled  Pulps.     Lap  Pulp.     Strength  or  Beating  Test.     Color 

Comparison.     Bleaching   Properties.     Loss  in  Weight   on   Bleaching. 

Sedimentation  Test. 

CHAPTER  XV 
PAPER  TESTING 386 

Microscopic    Examination.      Fibre    Content.      Unbleached    Sulphite. 

Physical  Tests.     Machine  Direction.     Wire  Side.    Weight  per  Ream. 

Thickness.      Bulk.      Opacity.      Gloss.      Tensile    Strength.      Stretch. 

Bursting  Strength.     Folding  Endurance.    Tearing  Test.    Absorbency. 

Volume   Composition.      Air   Permeability.      Grease-proof    Properties. 

Degree  of  Sizing.    Chemical  Tests.    Ash.    Retention.    Sizing  Materials. 

Rosin    Determination.      Paraffin.      Chlorine.      Free    Acid.      Sulphur. 

Amount   of    Coating.     Glue    or    Casein    Determination.     Unbleached 

Fibers.     Ground  Wood. 

CHAPTER  XVI 

PRINTING 429 

Definition.  Half-tone  Plates.  Lithography.  Paper  for  Different  Types 
of  Printing.  Choice  of  Inks.  Defects  and  their  Causes. 

APPENDIX  . .  444 


CHEMISTRY  OF 

PULP  AND    PAPER   MAKING 


CHAPTER  1 
CELLULOSE 

Even  at  the  present  day  the  chemistry  of  cellulose  cannot  be 
said  to  be  well  understood  though  much  energy  has  been  ex- 
pended in  the  attempt  to  discover  its  secrets  and  several  com- 
prehensive books  have  been  written  on  the  subject.1  This  state 
of  affairs  is  due  largely  to  its  colloidal  characteristics  which 
make  it  very  difficult  to  prepare  and  isolate  pure  compounds, 
and  render  it  practically  impossible  to  determine  its  molecular 
weight  or  to  ascertain  its  structural  formula.  For  these  reasons 
the  matter  in  the  present  chapter  is  confined  largely  to  state- 
ments of  facts  and  any  extended  discussion  of  theoretical  con- 
siderations is  intentionally  avoided. 

Physiological  and  Physical.  Cellulose  is  the  chief  product  of 
vegetable  life  and  forms  so  large  and  important  a  part  of  all 
plant  structures  that  its  formation  in  the  vegetable  world  is 
said  to  be  synonymous  with  growth.  It  is  practically  the  non- 
nitrogenous  skeleton  of  all  plants,  but  it  never  occurs  in  the 
plant  in  the  free  state,  being  associated  or  combined  with  fats 
and  waxes,  coloring  matters,  tannins,  etc. .  Because  of  its  physi- 
cal properties  and  its  relative  inertness  toward  the  attack  of 
chemicals  cellulose  is  of  enormous  commercial  importance,  form- 

1  Cross  and  Bevan:  Cellulose,  London,  1918;  Researches  on  Cellulose,  1895- 
1900,  London,  1901;  Researches  on  Cellulose,  1900-1905,  London,  1906;  Re- 
searches on  Cellulose,  1905-1910,  London,  1912.  Schwalbe:  Die  Chemie  der 
Cellulose,  Berlin,  1911. 

i 


CELLULOSE 


ing,  as  it  does,  the  basis  of  the  paper  making  and  textile  in- 
dustries, and  being  used  in  modified  forms  in  the  manufacture 
of  high  explosives,  artificial  silk,  and  celluloid  products. 

In  the  industrial  world  the  term  "cellulose"  is  generally 
understood  to  mean  the  portion  remaining  after  vegetable  tis- 
sues have  undergone  thorough  alternate  treatments  with  alka- 
line solvents  and  oxidizing  agents,  and  our  knowledge  of  the 
chemical  nature  of  cellulose  is  based  upon  a  study  of  materials 
isolated  by  more  or  less  drastic  treatment  of  this  nature  from 
fibrous  raw  materials.  The  typical  cellulose  is  that  obtained 
from  cotton  by  the  textile  bleaching  processes,  which  remove 
the  non-cellulose  substances  with  which  it  is  associated  in  the 
plant.  When  thus  prepared  it  is  a  white  substance,  with  a 
specific  gravity  of  about  1.45,  and  with  the  general  shape  and 
characteristics  of  the  fibres  from  which  it  was  prepared.  The 
individual  fibres  are  translucent  when  seen  under  the  microscope 
but  masses  of  them  are  more  or  less  opaque. 

Composition  and  Constitution.    The  elementary  composition 

of  purified  cotton  cellulose  is 

Per  cent 

Carbon 44-4 

Hydrogen 6.  2 

Oxygen .     49. 4 

which  corresponds  to  the  empirical  formula  C6H10O5.  This  does 
not  take  into  account  the  mineral  constituents  which  are  always 
present  to  a  greater  or  less  extent  even  in  the  most  highly  purified 
material.  The  ash  in  cotton  cellulose  is  usually  o.i  to  0.2 
per  cent  but  this  may  be  reduced  to  as  little  as  0.05  per  cent  by 
digestion  in  hydrofluoric  and  hydrochloric  acids  and  washing 
very  thoroughly  in  pure  water.  Ash  constituents,  on  the  other 
hand,  may  be  taken  up  by  cellulose  from  solutions  with  which 
it  is  in  contact  and  various  observers  have  shown  that  it  is 
capable  of  removing  from  solution  small  amounts  of  the  oxides 
of  aluminum,  iron,  chromium,  tin  and  lead.  Materials  taken 
up  in  this  manner  must  not  be  confounded  with  the  normal 
mineral  matter. 


CELLULOSE  AND  WATER  3 

As  already  mentioned  the  constitutional  or  structural  formula 
for  cellulose  has  not  yet  been  definitely  established  although 
many  investigators  have  attempted  to  solve  the  problem  and 
have  proposed  various  formulae  based  upon  its  known  reactions 
and  their  products.  Among  those  proposed  that  of  Green  l  is 
as  follows: 

CH  (OH)  •  CH  -  CH  (OH) 
\        \ 


CH  (OH)  •   CH  -  CH2 

This  is  intended  to  represent  cellulose  only  in  its  simplest  or 
unpolymerized  form,  as,  for  instance,  in  ammoniacal  copper 
solution.  The  cellulose  of  fibres  may  be  composed  of  a  number 
of  these  groups,  joined  by  means  of  their  oxygen  atoms,  or 
merely  a  physical  aggregate  of  a  number  of  molecules  of  the 
above  composition. 

By  other  authorities  cellulose  is  regarded  as  a  polycyclohexane 
derivative  or  as  an  essentially  labile  aggregate  which  assumes 
various  configurations  according  to  the  action  of  the  reagents 
employed.  It  is  closely  related  to  the  sugars,  starches,  glucose 
and  other  members  of  the  carbohydrate-  family. 

Cellulose  and  Water.  Water  at  ordinary  temperatures,  or 
even  at  a  temperature  corresponding  to  60  Ibs.  steam  pressure, 
has  no  action  on  cotton  if  air  is  excluded,  but  a  mixture  of  air 
and  steam  causes  rapid  disintegration  of  the  fibre.2 

Air  dry  cellulose  retains  variable  amounts  of  water  of  con- 
stitution according  to  the  humidity  and  temperature  of  the 
surrounding  atmosphere.  With  normal  cotton  this  constitu- 
v  tional  moisture  amounts  to  6  to  8  per  cent,  but  if  the  cotton  has 
been  hydrated  by  mercerization,  by  dissolving  and  reprecipi- 
tating,  or  by  prolonged  abrasive  action  in  the  presence  of  water, 
its  capacity  for  retaining  moisture  is  increased  and  such  air 

1  A.  G.  Green:  Z.  Farben-  u  Textil-Chem.,  1904,  3,  97-98. 

2  Hebden:  J.  Ind.  Eng.  Chem.,  1914,  6,  714-720. 


4  CELLULOSE 

dry  fibre  may  retain  9  to  10  per  cent  of  water.  Acids  which 
cause  condensation  (HC1,  HBr),  influence  this  change  in  the 
opposite  direction  and  the  resulting  product  has  a  lower  moist- 
ure capacity  —  3  to  5  per  cent  —  than  the  normal  cellulose. 
Since  the  atmospheric  humidity  affects  the  moisture  content  of 
cellulose  it  is  obviously  essential  to  have  some  fixed  standard 
for  commercial  transactions  and  for  the  paper  industry  it  is 
the  practically  universal  custom  to  consider  that  air  dry 
wood  pulp  contains  10  per  cent  of  moisture,  i.e.,  100  parts  of 
air  dry  pulp  will  yield  90  parts  of  bone  dry  fibre  when  dried  at 
100°  C. 

A  knowledge  of  the  normal  moisture  content  of  cellulose,  and 
of  the  products  made  therefrom,  is  of  importance  in  the  finishing 
and  commercial  handling  of  textile  goods,  while  in  the  paper 
industry  the  hydration  effect  of  the  beating  process  determines 
very  largely  the  character  of  the  paper  made.  In  the  latter 
industry  it  is  possible  to  make  from  the  same  raw  materials,  by 
varying  the  beating  process,  such  widely  different  products  as 
blotting  paper  and  grease-proof  parchment.  Ignorance  of  the 
relation  of  cellulose  and  atmospheric  humidity  is  also  one  of 
the  chief  causes  of  trouble  in  printing  plants  where  the  paper- 
maker's  product  becomes  the  publisher's  raw  material. 

The  difference  between  cellulose  hydrates  and  hydrocellulose 
is  one  which  is  often  not  well  understood  and  about  which 
much  confusion  is  likely  to  arise.  Hydrocelluloses  are  formed 
by  hydrolytic  action,  —  as  by  acids,  —  and  are  characterized 
by  the  presence  of  free  carbonyl  groups  which  reduce  Fehling's 
solution.  They  are  also  distinguished  by  an  abnormally  low 
moisture  content,  as  noted  above,  and  are  soluble  to  a  con- 
siderable extent  in  sodium  hydroxide  solutions  at  the  boiling 
temperature.  Cellulose  hydrates  may  be  formed,  either  with  or 
without  simultaneous  hydrolysis,  if  cellulose  is  acted  upon  by 
alkalis  or  other  chemicals  which  exert  a  swelling  action  in  the 
presence  of  water.  They  are  widely  different  in  their  properties 
but  possess  the  common  characteristics  of  a  high  moisture  con- 
tent, and  a  decreased  resistance  to  hydrolysis  by  acids.  Ost  and 


CELLULOSE  AND   SOLVENTS  5 

Westhoff  l  do  not  recognize  the  existence  of  "  water  of  hydra- 
tion"  as  distinct  from  hygroscopic  moisture  and  believe  that  the 
latter  can  be  accurately  determined  at  125°  C.  They  find  that, 
after  drying  at  120°  to  125°  C.,  mercerized  cotton,  normal  cotton, 
and  regenerated  cellulose  from  viscose  all  have  the  same  elemen- 
tary composition. 

Cellulose  and  Solvents.  Cellulose  is  insoluble  in  all  neutral 
solvent  liquids;  it  is,  however,  dissolved  by: 

1.  Concentrated  zinc  chloride  solutions  (40  to  50  per  cent 

ZnCl2),  when  heated  to  80  to  100  degs.,  or  at  lower 
temperatures  if  the  cellulose  has  previously  been 
hydrated. 

2.  Zinc  chloride  dissolved  in  twice  its  weight  of  hydro- 

chloric acid  (35  per  cent  HC1). 

3.  Solutions  of  cuprammonium  hydrate.2 

These  three  solvents  dissolve  cellulose  without  transforming  it 
into  other  compounds,  except  those  formed  by  the  action  of 
water,  and  from  solvents  i  and  3  the  cellulose  may  be  quanti- 
tatively regenerated  although  in  the  hydrated  condition.  When 
fibrous  celluloses  are  dissolved  by  these  reagents  they  pass 
through  various  stages  of  swelling  and  hydration  until  finally  a 
uniform  structureless  solution  is  obtained.  One  characteristic 
of  these  solutions  is  their  high  viscosity  which  limits  the  amount 
of  cellulose  which  can  be  dissolved  to  a  filterable  solution  to 
about  7  to  9  per  cent.  When  the  solution  of  cellulose  in  zinc 
chloride  is  forced  through  a  small  orifice  into  alcohol  the  cellu- 
lose is  precipitated  in  the  form  of  a  continuous  thread  of  trans- 
parent, solid  matter  containing  zinc  oxide  which  can  be  re- 
moved by  treating  with  hydrochloric  acid.  Water  also  causes 

1  Ost  and  Westhoff:   Chem.  Ztg.,  1909,  33,  197. 

2  These  may  be  prepared  conveniently  by  precipitating  cupric  hydrate  by 
adding  caustic  soda  to  a  cold  solution  of  copper  sulphate,  washing  the  precipitate 
thoroughly,  and  then  dissolving  it  in  strong  ammonia  (sp.  gr.  0.90).     The  solu- 
tion should  contain  2.5  to  3.5  per  cent  of  copper  (as  CuO  •  nH2O),  and  15  per  cent 
of  NH3  (as  NH4OH). 


O  CELLULOSE 

the  precipitation  of  cellulose  but  in  an  even  more  hydra  ted  state. 
The  solution  in  cuprammonium  is  not  at  all  stable,  the  cellulose 
being  readily  precipitated  by  alcohol,  sodium  chloride  and  other 
salts  of  the  alkalis,  and  even  by  sugar. 

Solutions  of  cellulose  find  technical  application  in  making 
threads,  which  are  carbonized  for  use  in  incandescent  lamps, 
and  in  the  manufacture  of  artificial  silk,  etc.  The  action  of 
solvents  is  also  utilized  in  making  "  vulcanized  fibre"  or  "press- 
board  "  where  a  web  of  fibre  is  passed  through  a  zinc  chloride  solu- 
tion and  then  wound  up  on  a  mandrel  or  drum.  After  removal 
from  the  drum  the  chemicals  are  thoroughly  washed  out  and 
the  sheets  are  dried  and  used  as  insulating  material  or  in  struc- 
tural work.  The  superficial  action  of  cuprammonium  solutions 
may  be  utilized  in  water-proofing  fabrics,  as  in  the  case  of  the 
"Willesden"  products,  but  if,  as  in  the  case  of  these  goods,  no 
attempt  is  made  to  remove  the  hydrated  copper,  the  products 
will  have  a  greenish  color. 

Cellulose  is  hydrated  and  dissolved  by  sulphuric  acid  of  a 
strength  of  67.0  to  78.0  per  cent  H2S04, —  approximately  H2S04  •  2 
H2O  —  H2S04  •  3  H20.  The  solution  is  syrupy  and  nearly  color- 
less and  if  diluted  at  once  the  cellulose  is  precipitated  as  a  gelati- 
nous hydrate.  This  reaction  is  the  basis  for  the  production  of 
"parchment  paper"  or  "  vegetable  parchment"  in  which  a  con- 
tinuous web  of  pure  cellulose  paper  is  passed  first  through  a  bath 
of  acid  and  then  at  once  into  water  which  stops  the  action  of  the 
acid  and  reprecipitates  the  cellulose  which  has  been  superficially 
dissolved.  After  washing  out  the  last  traces  of  acid  the  parch- 
mentized  web  is  treated  with  a  solution  of  glucose  or  glycerine 
and  dried.  The  glycerine  serves  to  retain  moisture  and  make 
the  paper  less  brittle  than  it  would  be  if  entirely  dried  out. 
Paper  treated  by  this  parchmentizing  process  suffers  consider- 
able linear  shrinkage,  sometimes  as  much  as  20  per  cent,  and 
also  loses  somewhat  in  weight. 

Deming  x  has  shown  that  cellulose  is  also  soluble  in  concen- 
trated aqueous  solutions  of  certain  salts,  such  as  antimony  tri- 
1  H.  G.  Deming:  J.  Am.  Chem.  Soc.,  1911,  33»  1515-1525. 


CELLULOSE  AND   SALTS  7 

chloride,  stannous  chloride  and  zinc  bromide.  Solutions  of  these 
salts,  and  many  others,  in  aqueous  hydrochloric  acid  dissolve 
cellulose  with  still  greater  ease.  From  such  acid  solutions  there 
are  obtained  by  reprecipitation  " modified  celluloses,"  amorphous 
products  which  have  distinct  reducing  properties  and  are  readily 
hydrolyzed. 

Although  ordinary  hydrochloric  acid,  and  even  that  of  sp.  gr. 
1.196,  are  incapable  of  dissolving  cellulose,  it  has  been  shown 
by  Willstatter  and  Zechmeister  l  that  complete  solution  rapidly 
takes  place  on  treating  cellulose  with  fuming  hydrochloric  acid 
of  a  specific  gravity  of  1.2  or  over.  Cotton  or  filter  paper  may 
be  dissolved  in  acid  of  sp.  gr.  1.209  in  about  10  seconds.  Im- 
mersing the  cotton  and  kneading  with  the  acid  enables  solu- 
tions of  7  to  15  per  cent  strength  to  be  obtained  according  to 
the  strength  of  the  acid.  Such  solutions  are  colorless  and  clear 
and  if  diluted  within  30  to  45  minutes  after  preparation  a  form 
of  cellulose  is  quantitatively  precipitated  and  the  solution  has 
no  cupric  reducing  power. 

Cellulose  and  Salts.  Because  of  its  colloidal  properties  cellu- 
lose forms  characteristic  combinations  with  inorganic  oxides, 
particularly  those  of  aluminum,  chromium,  iron,  tin  and  lead. 
These  oxides  are  taken  up  by  ceUulose  from  solutions  of  their 
salts  and  the  fibres  which  are  thus  mordanted  possess  increased 
affinity  for  coloring  matters.  In  the  case  of  iron  salts  sufficient 
ferric  oxide  may  be  taken  up  by  the  fibre  to  seriously  injure 
its  color. 

This  ability  to  absorb  oxides  doubtless  plays  some  part  in 
the  sizing  of  paper,  for  Schwalbe  and  Robsahm2  found  that 
unbleached  sulphite  wood  pulp  was  capable  of  absorbing  all 
the  alumina  present  in  3  per  cent  of  its  weight  of  aluminum 
sulphate.  This  corresponds  to  an  absorption  of  about  0.46 
per  cent  of  A1203  on  the  weight  of  the  fibre.  A  similar  investi- 
gation by  Sutermeister,3  working  on  bleached  fibres,  showed 

1  R.  Willstatter  and  L.  Zechmeister:  Ber.,  1913,  46,  2401-2412. 

2  C.  G.  Schwalbe  and  H.  Robsahm:  Wochbl.  Papierfabr.,  1912,  43,  1454-1457. 

3  E.  Sutermeister:  Pulp  Paper  Mag.  Can.,  1913,  n,  803. 


8  CELLULOSE 

that  the  weight  of  A12O3  absorbed,  based  on  the  bone  dry  fibre, 
was  0.23  to  0.29  per  cent  for  soda  poplar,  o.oo  to  0.17  per  cent 
for  sulphite  spruce,  and  o.io  to  0.13  per  cent  for  rag  fibres 
(cotton). 

Rassow1  finds  that  cotton  cellulose  is  capable  of  absorbing 
small  quantities  of  copper  from  dilute  solutions  of  copper  salts 
and  that  the  absorbed  metal  cannot  be  removed  by  washing. 
The  amount  absorbed  was  independent  of  the  time  of  contact, 
the  strength  of  the  solution  or  its  temperature.  Similar  results 
were  obtained  with  solutions  of  nickel  sulphate,  aluminum  sul- 
phate and  potassium  chloride. 

Decompositions  of  Cellulose.  Cellulose  is  broken  down  in  a 
number  of  different  ways  according  to  the  nature  of  the  attack- 
ing substance,  its  concentration  and  the  physical  conditions 
accompanying  the  reaction,  yet  the  study  of  these  decomposi- 
tions and  their  products  has  done  but  little  to  explain  the  con- 
stitution of  the  cellulose  molecule. 

Acids.  Dilute  sulphuric  and  hydrochloric  acids,  and  acids  in 
general,  attack  cellulose  with  varying  degrees  of  rapidity  de- 
pending on  the  temperature  and  the  concentration  of  the  acid. 
The  products  of  such  action  are  either  soluble  substances, 
chiefly  dextrins  and  dextrose,  or  insoluble-  bodies  generally 
termed  hydrocelluloses.  These  are  disintegrated  residues,  more 
or  less  retaining  the  form  of  the  original  fibres,  and  they  differ 
from  cellulose  in  the  presence  of  free  aldehydic  groups  and  in 
the  ease  with  which  they  are  acted  on  by  alkalis.  According 
to  Griffin  and  Little 2  hydrocellulose  absorbs  oxygen  when 
heated,  even  at  so  low  a  temperature  as  50  degs.,  and  after 
being  kept  for  some  hours  at  80  to  100  degs.  in  contact  with 
air  is  converted  into  dark  colored  compounds  which  are  soluble, 
in  water.  Hydrocellulose,  unlike  oxycellulose,  does  not  attract 
basic  dyes. 

Ville  and  Mestrezat 3  found  that  dilute  hydrofluoric  acid  had 

1  B.  Rassow:  Z.  angew.  Chem.,  1911,  24,  1127. 

2  Griffin  and  Little:  Chemistry  of  Paper  Making,  114. 

3  Ville  and  Mestrezat:  Compt.  rend.,  1910,  150,  783. 


ALKALIS 

little  effect  on  cellulose  but  that  at  40  to  50  per  cent  strength 
considerable  dextrose  was  formed.     Ost  and  Wilkening1  have 
confirmed  Flechsig's  claim  that  98  per  cent  of  the  cellulose  may 
be  converted  into  dextrose  by  suitable  treatment  with  acid.    \ 
This  result  cannot  be  reached  by  the  action  of  dilute  acids  at    / 
high  temperatures  because  the  dextrose  formed  is  destroyed    ) 
either  by  reverse  condensation  or  by  conversion  into  acids.  ( 
According  to  Willstatter  and  Zechmeister 2  cellulose  may  be 
completely  hydrolyzed  by  hydrochloric  acid  acting  in  the  cold 
for  a  period  of  i  to  2  days  and  a  yield  of  95  to  96  per  cent  of 
the  theoretical  amount'  of  dextrose  may  be  obtained.     Cun- 
ningham 3  has  reinvestigated  the  relationship  of  cellulose  to 
dextrose  and  has  failed  to  confirm  the  results  of  Ost  and  Wilken- 
ing or  Willstatter  and  Zechmeister;   he  considers  their  conclu- 
sions based  on  insufficient  data  and  thinks  that  the  investiga- 
tions have   thrown  very  little  light  on   the  structure  of  the 
cellulose  complex. 

The  formation  of  friable  hydrocelluloses  by  acids  is  of  great 
importance  industrially  for  upon  it  is  based  the  carbonization 
process  for  separating  cotton  from  wool  in  which  the  mixed 
goods  are  immersed  in  acid  and  allowed  to  dry  without  washing. 
This  con  verts, the  cotton  into  hydrocellulose  which  can  be  re- 
moved by  dusting,  leaving  the  wool  behind  in  suitable  condition 
for  future  use. 

Alkalis.  In  the  presence  of  air  caustic  soda  solutions  of  a 
strength  of  10  to  20  grams  per  liter  rapidly  disintegrate  cotton 
fibre  at  a  temperature  corresponding  to  10  Ibs.  steam  pressure. 
When  air  is  excluded  cellulose  is  only  slightly  acted  on  by  dilute 
solutions  of  alkalis  even  at  high  temperatures.  Caustic  soda 
solutions  of  12  per  cent  strength,  and  over,  combine  with  cellu- 
lose at  ordinary  temperatures,  causing  marked  changes  in  physical 
structure  but  not  breaking  up  the  molecular  grouping.  Still 
stronger  solutions,  at  temperatures  as  high  as  180  degs.,  form 

1  Ost  and  Wilkening:  Chem.  Ztg.,  1910,  34,  461. 

2  Willstatter  and  Zechmeister:  Ber.,  1913,  46,  2401. 

3  Cunningham:  Chem.  Soc.  Trans.,  1918,  113,  173-181. 


V 


10"  CELLULOSE 

merely  soluble  modifications  which  on  diluting  and  acidifying 
are  precipitated  in  colloidal  form.  At  still  higher  temperatures 
(250  degs.)  and  with  larger  proportions  of  alkaline  hydroxides 
cellulose  is  broken  down  largely  into  acetic  and  oxalic  acids. 

Oxidants.  From  the  condition  of  papers  and  textiles  which 
have  for  centuries  been  exposed  to  all  ordinary  atmospheric 
conditions,  it  seems  fair  to  assume  that  oxidation  due  to  the 
surrounding  atmosphere  is  extremely  slight,  a  fact  which  is  of 
the  utmost  importance  technically.  Cellulose  is  also  quite  re- 
sistant to  oxidizing  agents  in  dilute  solutions,  a  circumstance 
which  makes  it  possible  to  remove  impurities  of  a  colored  nature 
without  at  the  same  time  destroying  the  fibres.  If,  however, 
the  concentration  of  the  oxidant  exceeds  the  limit  of  resistance 
of  the  cellulose  destructive  oxidation  takes  place  with  the  forma- 
tion of  products  of  low  molecular  weight,  principally  oxalic 
and  carbonic  acid.  Not  all  of  the  products  are  soluble,  how- 
ever, as  a  portion  remains  undissolved  and  retains  more  or  less 
of  the  original  form  of  the  fibres.  These  insoluble  residues  are 
known  as  oxy celluloses.  They  contain  free  aldehydic  groups, 
are  easily  hydrolyzed,  and  yield  some  furfural,  C4H3O  •  COH, 
on  boiling  with  hydrochloric  acid  of  sp.  gr.  1.06.  They  are 
white,  friable  substances  and  contain  less  carbon  and  more 
oxygen  than  cellulose.  No  method  is  known  of  restoring  to  its 
original  condition  fibre  which  has  been  converted  to  oxycellulose. 

The  results  of  the  oxidation  of  cellulose  are  not  always  the 
same,  as  they  depend  on  the  nature  of  the  oxidant,  its  concen- 
tration, the  temperature  at  which  it  acts  and  on  accompanying 
reactions  of  a  hydrolytic  nature.  With  concentrated  solutions 
of  hypochlorites  or  hypobromites  there  is  some  formation  of 
chloroform  and  carbon  tetrachloride  or  the  corresponding  bro- 
mine compounds.  The  action  of  nitric  acid  (sp.  gr.  i.i  to  1.3) 
at  elevated  temperatures  results  in  the  formation  of  a  series  of 
oxycelluloses  which  are  characterized  by  yielding  less  furfural 
than  those  formed  by  the  action  of  chromic  acid.  With  chromic 
acid  the  degree  of  action  depends  on  the  proportion  of  the  re- 
agent and  on  the  hydrolytic  action  of  the  associated  mineral 


OXIDANTS  II 

acid.  The  oxycelluloses  produced  yield  comparatively  large 
amounts  of  furfural.  The  ultimate  result  of  the  action  of 
chromic  acid  in  the  presence  of  sulphuric  acid  is  complete  com- 
bustion to  CO2  and  H2O,  a  reaction  upon  which  are  based  quan- 
titative analytical  methods. 

After  a  study  of  the  results  obtained  in  bleaching  Cross  and 
Bevan  1  suggested  the  possibility  of  the  formation  of  a  cellulose 
peroxide.  Similar  phenomena  were  observed  by  Ditz2  in  the 
case  of  cellulose  which  had  been  gradually  heated  to  80°  C.  in 
an  acid  solution  of  a  persulphate  and  then  slowly  cooled,  while 
according  to  Cunningham  and  Doree,3  ozone  rapidly  attacks 
cotton  with  the  formation  of  cellulose  peroxide  which  is  decom- 
posed by  water  at  80°  C. 

Oxycelluloses  reduce  Fehling's  solution  and  on  this  property 
is  based  Schwalbe's  method  for  determining  the  degree  of  'bleach- 
ing of  fibres;  as  hydrocelluloses  reduce  Fehling's  solution,  the 
method  also  shows  the  effects  of  any  coincident  hydrolytic 
action.  The  determination  of  the  degree  of  bleaching,  or,  as  it 
is  frequently  called,  the  "  copper  number,"  has  proved  of  con- 
siderable assistance  in  technical  investigations  and  the  procedure 
employed  by  Schwalbe 4  is  about  as  follows :  Two  portions  of 
about  three  grams  each  are  weighed  out,  of  which  one  is  used 
for  the  determination  of  the  percentage  of  moisture.  The  other 
is  reduced  to  a  finely  divided  condition  and  mixed  with  300  c.c. 
of  water  and  100  c.c.  of  Fehling's  solution.  This  is  boiled  in  a 
flask  for  exactly  15  minutes,  using  a  reflux  condenser  to  keep 
the  volume  constant  and  a  stirrer  to  maintain  continuous  agi- 
tation. Precautions  must  be  taken  to  prevent  overheating 
the  walls  of  the  flask  as  drops  of  the  liquid  or  portions  of  the 
moist  fibre  which  spatter  onto  them  may  be  decomposed  with 
formation  of  products  affecting  the  results.  After  boiling,  the 

1  Cross  and  Bevan:  Z.  angew.  Chem.,  1906,  19,  2101. 

2  Ditz:  Chem.  Ztg.,  1907,  31,  833. 

3  Cunningham  and  Doree:  Chem.  Soc.  Proc.,  1912,  28,  38. 

4  Schwalbe:  Ber.,  1907,  40,  1347-1351;   Z.  angew.  Chem.,  1910,  23,  924-928; 
Z.  angew.  Chem.,  1914,  27,  567-568. 


12  CELLULOSE 

liquid  is  filtered  while  hot  by  means  of  the  suction  pump,  and 
the  fibrous  residue  is  washed  with  hot  water.  The  precipitated 
copper  is  dissolved  from  the  fibre  by  nitric  acid,  the  final  traces 
being  removed  by  digestion  with  ammonia,  and  the  copper  then 
determined  by  electrolysis. 

As  the  presence  of  hydrated  or  modified  celluloses  causes  the 
precipitation  of  copper  hydroxide  by  adsorption  the  "  copper 
number"  obtained  as  above  must  be  corrected  by  deducting 
the  "  hydrate  copper  value"  which  is  determined  by  immersing 
a  fresh  portion  of  the  cellulose  in  cold  Fehling's  solution  for 
45  minutes  and  determining  the  copper  as  before. 

Ferments.  Certain  organisms  affect  the  complete  disruption 
of  the  cellulose  molecule,  or  aggregate,  the  chief  products  being 
hydrogen,  methane,  carbon  dioxide  and  fatty  acids.  Such  bac- 
terial fermentation  on  a  large  scale  in  the  soil  is  one  of  the  chief 
processes  by  which  the  cellulosic  portion  of  plant  remains  is 
resolved  into  simpler  products.  In  the  digestive  organs  of  her- 
bivorous animals  cellulose  is  broken  down"  by  similar  fermenta- 
tive processes,  apparently  with  the  formation  of  simpler  sub- 
stances of  high  nutritive  value,  which  are  readily  assimilated. 
In  addition  to  these,  gaseous  products  are  also  formed,  carbon 
dioxide,  methane,  and  sometimes  hydrogen  being  produced. 

Omelianski  concluded  that  the  organisms  causing  decompo- 
sition of  cellulose  were  anaerobic,  but  Kellerman  and  McBeth  1 
have  succeeded  in  isolating  three  cellulose-destroying  organisms 
which  act  most  rapidly  under  aerobic  conditions.  None  of 
these  causes  evolution  of  gas.  In  addition  they  have  isolated 
eleven  other  species  of  cellulose-destroying  bacteria  all  of  which 
were  facultative  anaerobes  fermenting  cellulose  most  rapidly 
under  aerobic  conditions. 

Heat.  When  cellulose  is  heated  above  250°  C.  very  complex 
decompositions  take  place  and  among  the  products  are  charcoal, 
acetic  acid,  methyl  alcohol,  acetone,  furfural,  carbon  monoxide 
and  carbon  dioxide.  The  proportions  of  these  substances  vary 
with  the  temperature  and  the  rate  and  duration  of  heating. 
1  Kellerman  and  McBeth:  Centr.  Bakt.  Parasitenk,  II,  34,  485-494. 


NITRATES  13 

When  cellulose  was  distilled  destructively  in  such  a  way  that  a 
temperature  of  100  degs.  was  reached  in  ij  hours  and  503  degs. 
in  7  to  8  hours,  Bantlin  1  found  the  following  products,  the  per- 
centages being  given  on  the  weight  of  the  dry  substance  used: 

Per  cent 

Coke 32.9 

Water 31.7 

Tar..... 3.25 

Acetic  acid 3.  28 

Aldehydes 5. 82 

Ketones o.  n 

Carbon  dioxide 1 1 .  26 

Carbon  monoxide 4.  78 

Ethylene o.  24 

Hydrogen o.  02 

Ethane o.  35 

Methane o.  68 

Undetermined 5.  23 

During  the  course  of  this  distillation  there  was  an  exothermic 
reaction  at  250  to  300  degs.  which  was  complete  at  320  degs. 

Compounds  of  Cellulose.  Cellulose  is  not  a  substance  of 
great  reactivity  yet  there  are  a  number  of  its  compounds  which 
are  of  very  great  commercial  importance.  Most  of  these,  it  is 
true,  do  not  vitally  concern  the  paper  maker,  yet  a  discussion 
of  the  properties  of  cellulose,  no  matter  how  concise,  would  be 
quite  incomplete  unless  they  were  at  least  briefly  mentioned. 
Moreover,  a  knowledge  of  how  they  are  formed  and  of  their 
characteristics  is  of  distinct  assistance  in  enabling  the  student 
to  secure  a  better  perspective  of  paper  making  processes  in 
their  relation  to  those  of  other  industries. 

Nitrates.  These  esters  are  formed  by  direct  reaction  with 
nitric  acid,  usually  mixed  with  sulphuric  acid,  and  the  compo- 
sition and  properties  of  the  resulting  nitrate  depend  largely  on 
the  proportions  of  the  two  acids  and  on  the  amount  of  water 
with  which  they  are  mixed.  Crane  and  Joyce,2  using  a  mixture 

1  G.  Bantlin:  J.  Gasbel.,  1914,  57>  32  and  55- 

2  Crane  and  Joyce:  J.  Soc.  Chem.  Ind.,  1910,  29,  540. 


14  CELLULOSE 

containing  57  to  67  per  cent  of  sulphuric  acid,  16  to  6  per  cent 
of  nitric  acid  and  25  to  27  per  cent  of  water,  and  nitrating  for 
short  times  have  prepared  products  with  as  little  as  3.5  to  4.5 
per  cent  of  nitrogen.  These  are  pasty,  gelatinous  masses,  in- 
soluble in  all  nitrocellulose  solvents,  but  readily  soluble  in 
solutions  of  caustic  alkalis. 

When  stronger  acids  are  employed  the  nitrates  formed  con- 
tain more  nitrogen  up  to  a  limit  of  about  14  per  cent  which 
corresponds  to  the  trinitrate,  C&HyOsCNC^s.  This  nitrate, 
which  is  the  most  explosive  gun-cotton,  may  be  prepared  by 
treating  cotton  with  a  mixture  of  3  parts  of  nitric  acid  (sp.  gr. 
1.5)  and  i  part  of  sulphuric  acid  for  about  24  hours  at  10°  C. 
The  unstable  mixed  esters,  containing  both  nitric  and  sulphuric 
groups,  are  formed  as  an  intermediate  stage  in  the  reaction  and 
the  NO3  groups  finally  replace  the  HSO4  groups.  It  is  con- 
sidered that  traces  of  the  mixed  ester  remaining  in  the  finished 
product  are  often  responsible  for  its  instability.  In  this  reaction 
i oo  parts  of  cellulose  yield  about  1 70  parts  of  the  nitrate.  Nitra- 
tion under  these  conditions  does  not  visibly  alter  the  physical 
structure  of  the  cellulose.  The  trinitrate  is  insoluble  in  alcohol, 
ether,  mixtures  of  the  two,  glacial  acetic  acid  or  methyl  alcohol; 
it  is  very  slowly  soluble  in  acetone.  The  next  lower  members, 
corresponding  approximately  to  the  dinitrate,  CeHgC^NOs^, 
.are  soluble  in  ether-alcohol,  acetic  ether,  acetic  acid  and  methyl 
alcohol,  while  the  mononitrate,  C6H9O5NO3  is  very  soluble  in 
ether-alcohol,  acetic  ether  and  absolute  alcohol.  A  consider- 
able number  of  nitrates  have  been  formed  but  it  has  proved 
very  difficult  to  isolate  any  one  of  them  in  a  pure  condition  and 
from  a  careful  study  of  the  work  of  G.  Lunge,1  Cross  and  Bevan 
have  reached  the  conclusion  that  "the  stages  of  nitration  of 
cellulose  are  not  molecular  stages,,  but  represent  progressive 
increments  of  the  esterifying  groups  in  a  mass-aggregate,  which 
is  the  reacting  unit."  2 

The  general  properties  of  the  cellulose  nitrates  are:    (i)  nitric 

1  G.  Lunge:  J.  Am.  Chem.  Soc.,  1901,  23,  527. 

2  Cross  and  Bevan:  Researches  on  Cellulose,  II,  1900-1905,  44. 


GUN-COTTON  15 

acid  may  be  removed  by  warming  with  alkaline  solutions,  the 
amount  removed  depending  on  the  concentration  of  the  alkali; 
(2)  nearly  all  of  the  nitric  acid  is  expelled  by  treatment  with 
cold  concentrated  sulphuric  acid;  (3)  boiling  with  ferrous  sul- 
phate and  hydrochloric  acid  drives  off  the  nitrogen  as  nitric 
oxide;  (4)  alkaline  sulphydrates,  ferrous  acetate  and  numerous 
other  substances  convert  the  nitrate  into  ordinary  cellulose. 

The  various  cellulose  nitrates  find  many  very  important  com- 
mercial uses.  Mixed  with  castor  oil  they  are  extensively  used 
in  the  manufacture  of  artificial  leather.  In  solution  in  ether- 
alcohol  cellulose  nitrate  is  employed  in  the  manufacture  of 
artificial  silk  by  the  Chardonnet  process,  the  fibre  being  finally 
denitrated  by  treatment  with  ammonium  sulphide  to  render  it 
less  inflammable.  The  fibrous  nitrates  may  be  reduced  to  plastic 
masses  by  kneading  with  solvents  and  in  this  condition  may  be 
formed  into  articles  of  any  desired  shape.  As  films  they  find 
use  in  photography,  as  the  carrier  for  the  emulsion;  in  the  solid 
form,  after  the  incorporation  of  camphor,  they  are  spoken  of  as 
celluloid  or  xylonite  and  find  innumerable  uses. 

The  nitrogen  content  of  the  nitrates  for  various  purposes  is 
given  by  Mork  1  as  follows:  Celluloid  and  films  for  moving  pic- 
tures about  10 J  to  ii J  per  cent;  varnishes  and  lacquers  nj  to 
12  per  cent;  for  powder  purposes  12  to  12 J  per  cent;   and  for  / 
gun-cotton  13  to  14  per  cent.     In  the  higher  nitrates  the  pro- 
portion of  oxygen  is  such  that  upon  decomposition  the  products    j^j 
are  entirely  gaseous  and  it  is  upon  this  property  that  their  use 
as  explosives  depends. 

Gun-cotton.  Because  of  the  similarity  between  many  of  the 
methods  used  in  paper  making  and  those  in  the  manufacture  of 
gun-cotton  a  very  brief  description  of  the  methods  used  in  the 
latter  industry  may  be  of  interest. 

Cotton  is  still  practically  the  only  cellulose  used  although  it 
has  apparently  recently  been  demonstrated  that  certain  grades 
of  wood  pulp  will  make  acceptable  substitutes.  The  cotton  is 
obtained  in  the  form  of  spinning  wastes  or  of  the  short  fibres 

1  Mork:  J.  Frank.  Inst.,  Sept.,  1917. 


16  CELLULOSE 

from  the  seeds  known  as  linters.  Where  spinning  wastes  are 
used  the  fibres  are  first  degreased  by  treatment  with  some 
solvent,  then  boiled  with  caustic  soda,  bleached  with  bleaching 
powder  solution  or  with  calcium  sulphide,  washed,  neutralized 
with  sulphuric  or  hydrochloric  acid,  again  washed,  and  finally 
dried.  It  should  contain  no  chlorides,  sulphates,  oxycellulose 
or  hydrocellulose,  but  it  often  contains  mechanical  impurities 
such  as  wood,  string,  colored  threads,  metal,  etc.,  and  to  re- 
move these  it  is  hand  picked  as  it  passes  along  a  conveyor  to  a 
"willow"  which  opens  out  the  lumps  and  knots.  After  leaving 
the  "  willow"  it  is  again  hand  picked  and  then  is  dried  by  hot 
air,  weighed  in  charges  of  the  desired  size  and  cooled  in  closed 
containers. 

Various  methods  of  nitration  are  in  use  but  all  depend  on 
the  immersion  of  small  quantities  of  cotton  in  comparatively 
large  volumes  of  mixed  nitric  and  sulphuric  acid.  The  time 
of  nitration  varies  from  30  minutes  to  24  hours  according  to  the 
method  employed.  The  speed  of  nitration  increases  rapidly 
with  rise  of  temperature,  but  the  yield  decreases  although  the 
nitrogen  content  of  the  product  remains  practically  constant. 
After  nitration  the  excess  acid  is  removed  by  centrifugal  action 
and  the  fibrous  nitrate  is  washed  by  rinsing  and  is  then  boiled 
either  with  water  alone  or  with  the  addition  of  a  very  little 
alkali  in  order  to  remove  traces  of  free  acid  and  to  decompose 
and  dissolve  unstable  impurities.  This  boiling  operation,  with 
intermediate  washings  with  cold  water,  sometimes  lasts  4  to  5 
days. 

The  next  operation  is  that  of  pulping  the  washed  nitrate; 
this  is  done  in  beaters  very  similar  to  those  used  in  paper  manu- 
facture but  slightly  modified  in  order  that  thorough  agitation 
and  no  settling  may  take  place.  During  the  pulping  the  fibre 
is  reduced  in  length  and  is  at  the  same  time  washed  continu- 
ously with  hot  water  in  order  to  remove  the  last  traces  of  acid. 
Further  washing  is  given  by  agitation,  settling  and  removing 
suspended  impurities  after  which  enough  alkali  is  added  to 
leave  in  the  finished  gun-cotton  i  to  2  per  cent  of  alkaline  matter 


ACETATES  17 

calculated  as  CaCO3.  The  pulp  is  then  run  into  moulds  with 
bottoms  of  fine  wire  gauze  and  the  water  removed  by  suction 
and  by  hydraulic  pressure.  The  slabs  thus  formed  are  used 
wet  or  after  drying  according  to  the  purpose  for  which  they  are 
desired. 

For  the  manufacture  of  smokeless  powder  the  washed  pulp 
is  screened  and  then  dried  by  centrifugal  action;  it  still  con- 
tains much  water  and  this  is  removed  by  treatment  with  ethyl 
alcohol.  Finally  a  little  ether,  or  other  volatile  solvent,  is 
kneaded  in  which  produces  a  paste  ready  for  the  blocking 
operations.  The  solvents  are  removed  during  drying  so  that 
very  little  remains  in  the  finished  product. 

Nitrites.  When  viscose  silk  is  treated  with  nitrous  gases  in 
the  presence  of  nitric  acid  nitrites  of  cellulose  are  formed.  They 
are  not  soluble  in  water,  alcohol,  acetone,  ether,  chlorofprm,  or 
ethyl  acetate.  Nitrogen  is  given  off  slowly  at  ordinary  tem- 
peratures and  rapidly  on  heating.  Nitrites  are  liable  to  occur 
in  nitrocellulose  and  cause  rapid  deterioration.1 

Acetates.  Cellulose  acetates  are  formed  when  cellulose  is 
treated  with  acetic  anhydride  under  quite  widely  varying  con- 
ditions. The  monoacetate,  which  is  formed  at  no  degs.,  is 
insoluble  in  all  neutral  solvents  and  in  the  solvents  of  cellulose. 
At  140  to  1 60  degs.  higher  acetates  are  formed,  accompanied 
by  solution  in  the  reaction  mixture,  while  in  the  presence  of 
catalytic  agents —  zinc  chloride,  sulphuric  acid,  or  phosphoric 
acid,  for  instance —  the  reactions  take  place  at  much  lower 
temperatures,  due  doubtless  to  the  formation  of  hydrocellulose 
which  acetylates  more  rapidly  than  the  normal  cellulose.  Ost,2 
who  has  studied  the  formation  of  acetates  by  three  different 
processes,  finds  that  all  yield  the  triacetate,  CeHyC^C^sC^s, 
but  at  the  same  time  he  doubts  the  existence  of  a  triacetate  of 
normal  cellulose  and  considers  these  compounds  as  derivatives 
of  a  series  of  hydrocelluloses.  This  feature  of  preliminary 
hydrolysis  seems  to  be  one  of  the  essentials  of  acetate  forma- 

1  Nicolardot  and  Chertier:  Compt.  rend.,  1910,  151,  719-722. 

2  Ost:  Z.  angew.  Chem.,  1906,  19,  993. 


i8  CELLULOSE 

tion.  Acetylation  of  the  fibrous  celluloses  without  appreciable 
structural  change  may  be  accomplished  by  diluting  the  reagents 
with  hydrocarbons. 

The  higher  acetates  are  soluble  in  acetone,  phenol  and  chloro- 
form and  the  solutions  are  of  high  viscosity.  Boiling  the  ace- 
tates with  alkaline  solutions  splits  off  the  acetyl  groups  and 
the  cellulose  is  regenerated. 

In  contrast  to  the  nitrates  the  acetates  are  non-explosive,  and 
since  they  can  be  dissolved  by  appropriate  volatile  solvents  to 
homogeneous  solutions  they  are  admirably  adapted  for  use  in 
the  preparation  of  films,  threads,  etc.  Commercial  acetates 
are  on  the  market  in  the  fibrous,  granular  or  powdered  forms 
or  in  solutions  of  various  viscosities.  They  are  used  for  nearly 
all  purposes  for  which  the  nitrate  is  used  except  for  explosives 
and  their  use  would  be  still  more  extended  but  for  the  fact  that 
their  cost  of  manufacture  is  appreciably  greater  than  that  of 
the  nitrate.  It  is  interesting  to  note  that  acetate  silk  is  the 
only  one  in  which  the  final  product  retains  the  ester  composi- 
tion, since  in  other  cases  reactions  take  place  which  leave  the 
thread  simply  as  hydrated  cellulose.  This  is  probably  the 
reason  why  wetting  reduces  the  strength  of  acetate  silk  so  much 
less  than  it  does  the  other  kinds. 

Cellulose-Sulphuric  Esters.  The  action  of  concentrated  sul- 
phuric acid  on  cellulose  causes  the  formation  of  a  series  of  esters 
which  have  been  described  as  cellulose  sulphuric  acids  but 
which  are  more  probably  derivatives  of  resolution  products. 
The  first  stage  of  the  reaction  is,  according  to  Stern,1  the  forma- 
tion of  a  disulphuric  ester,  CeHgOsCSO^H)^  which  is  soluble  in 
water  while  its  calcium  barium  and  lead  salts  are  insoluble  in 
alcohol.  This  reaction  of  cellulose  and  sulphuric  acid  is  of 
great  importance  in  processes  of  esterification,  where  the  acid 
acts  as  a  catalyst,  first  combining  with  the  cellulose  and  then 
being  replaced  by  the  ester  forming  groups.  In  the  case  of 
nitrates  and  acetates  this  substitution  is  never  quite  complete, 
and  traces  of  SO4H  remain  fixed  in  both  compounds.  The 

1  Stern:  J.  Chem.  Soc.,  1895,  i,  74~9o- 


FORMATES  19 

presence  of  such  residues  in  the  nitrate  renders  it  unstable  and 
its  removal  is  one  of  the  chief  reasons  for  the  extended  boiling 
and  washing  treatments  which  gun-cotton  undergoes. 

Mixed  Esters.  As  may  be  concluded  from  the  above  the 
joint  action  of  sulphuric  acid  with  other  esterifying  agents  can 
result  in  the  formation  of  mixed  esters  containing  SO4H  groups 
as  well  as  other  negative  groups.  In  this  way  aceto-sulphates 
are  formed  by  the  action  of  acetic  anhydride,  glacial  acetic 
acid  and  sulphuric  acid.1  These  contain  from  5  to  25  per  cent 
of  combined  SO4  and  may  be  grouped  in  three  classes  ac- 
cording to  their  physical  properties.  Those  with  most  864  are 
soluble  in  water,  the  others  in  acetone  or  dilute  alcohol.  In  a 
similar  way  aceto-nitro-sulphates  and  nitro-benzoates  have  been 
formed. 

Benzoates.  The  action  of  benzoyl  chloride  in  the  presence  of 
alkali  hydroxides  results  in  the  formation  of  cellulose  benzoates. 
The  monobenzoate  is  formed  with  only  slight  structural  changes 
when  cellulose  is  treated  with  a  10  per  cent  solution  of  caustic 
soda  and  shaken  with  benzoyl  chloride.  The  dibenzoate  is 
formed  in  the  presence  of  15  per  cent  caustic  soda  solution,  the 
fibrous  celluloses  being  disintegrated,  as  the  dibenzoate  is  an 
amorphous  substance.  This  compound  is  soluble  in  acetic  acid 
and  chloroform. 

Formates.  Formylated  cellulose  may  be  made  by  treating 
hydrocellulose  with  formic  acid  in  the  presence  of  zinc  chloride.2 
Its  slight  solubility  in  organic  solvents  and  its  lack  of  thread, 
and  film-forming  ability  make  it  rather  unpromising.  Accord- 
ing to  German  patents,3  solutions  of  the  following  compounds 
may  be  used  as  solvents  of  cellulose  formate:  iodides  and  bro- 
mides of  the  alkali  metals,  metallic  nitrates  as  well  as  those  of 
ammonia  and  the  alkaline  earths,  cupric  chloride,  soluble  bichro- 
mates, alkali  xanthates,  aniline  salts  and  alkali  salts  of  aromatic 
mono-  and  polysulphonic  acids. 

1  Cross,  Bevan  and  Briggs:  Berl.  Ber.,  1905,  38  and  1859. 

2  Worden:  J.  Soc.  Chem.  Ind.,  1912,  31,  1064. 

8  Ger.  Pats.  266,600  and  267,577,  July  5,  1912,  and  Feb.  26,  1913. 


20  CELLULOSE 

Alkali-Cellulose.  The  action  of  solutions  of  sodium  hydroxide 
of  12  to  15  per  cent  strength  causes  considerable  change  in  the 
structure  of  fibrous  celluloses,  particularly  cotton  which  is 
changed  from  a  flattened  twisted  ribbon  with  a  large  central 
canal  to  a  thickened  cylinder  in  which  the  canal  shows  very 
little.  When  this  action  takes  effect  on  cloth  there  is  a  con- 
siderable shrinkage  both  in  length  and  width  but  at  the  same 
time  the  cloth  gains  in  strength.  The  amount  of  shrinkage 
varies  with  the  strength  of  solution  employed;  it  is  practically 
uniform  for  solutions  of  sp.  gr.  i.oo  to  i.io,  while  there  is  a 
sudden  increase  at  sp.  gr.  i.io  to  1.12.  Between  this  point  and 
sp.  gr.  1.225  there  is  a  relatively  rapid  increase  in  shrinkage 
but  beyond  the  latter  point  the  shrinkage  again  diminishes.  If 
the  goods  are  kept  under  tension  during  the  reaction  the  physi- 
cal changes  give  to  the  material  a  peculiar,  silky  lustre.  This 
reaction  is  spoken  of  as  mercerization  from  the  name  of  Mercer 
by  whom  it  was  first  discovered. 

The  effects  thus  obtained  are  due  to  a  definite  chemical  com- 
bination of  cellulose  and  caustic  soda  in  the  proportions  CeHioOs 
to  2  NaOH,  accompanied  by  combination  with  water.  This 
compound  is  entirely  dissociated  by  water,  the  alkali  being 
recovered  unchanged  while  the  cellulose  remains  in  the  hydrated 
condition.  When  it  is  treated  with  alcohol  equilibrium  is 
reached  when  part  of  the  alkali  is  removed,  the  residue  being 
Ci2H20Oio-NaOH.1 

Cellulose-Sulpho-Carbonates.  The  above  mentioned  alkali- 
cellulose-hydrate,  containing  30  per  cent  cellulose,  15  per  cent 
caustic  soda  and  55  per  cent  water,  is  the  first  step  in  the  forma- 
tion of  cellulose-sulpho-carbonate  which.is  also  known  as  sodium- 
cellulose-xanthate  and  viscose.  This  compound  is  prepared  by 
acting  on  the  alkali  cellulose  with  carbon  disulphide  at  ordinary 
temperatures.  In  practice  bleached  cotton  or  wood  pulp  is 
treated  with  an  excess  of  15  to  18  per  cent  caustic  soda  solution 
and  then  pressed  until  it  retains  i\  to  3  times  its  weight  of  the 
solution.  This  is  then  treated  in  a  closed  vessel  with  carbon 
1  Cross  and  Bevan:  Researches  on  Cellulose,  II,  p.  13. 


CELLULOSE-SULPHO-CARBONATES  21 

disulphide  amounting  to  about  half  the  vveight  of  the  cellulose. 
At  the  end  of  about  three  hours  at  ordinary  temperatures  water 
is  added  and  the  mass  allowed  to  stand  for  some  hours  to  com- 
plete its  hydration;  on  stirring  a  homogeneous  solution  results, 
which  may  be  diluted  to  any  desired  degree. 

The  impure  compound  is  yellow  in  color  due  to  by-products 
of  the  reaction,  but  the  pure  material,  which  may  be  prepared 
by  treating  the  crude  solution  with  alcohol  or  saturated  brine, 
is  obtained  in  the  form  of  greenish  white  flocculent  masses. 
These  redissolve  in  water  to  a  faintly  yellow  solution  and  from 
such  solutions  the  xanthates  of  the  heavy  metals  may  be  pre- 
cipitated by  adding  solutions  of  the  corresponding  heavy  metal 
salts. 

Viscose  solutions  may  be  evaporated  at  low  temperatures  to 
solids  which  are  completely  resoluble  in  water,  but  if  the  solu- 
tions are  heated  to  70  to  80  degs.  they  thicken  and  at  80  to  90 
degs.  coagulation  takes  place  very  rapidly.  Mineral  acids  neu- 
tralize the  total  alkali  in  the  viscose  and  cause  precipitation  of 
hydrated  cellulose  while  organic  acids  are  not  sufficiently  strong 
to  decompose  the  sulpho-carbonate. 

The  most  characteristic  property  of  viscose  is  its  spontaneous 
decomposition  with  formation  of  hydrated  cellulose,  caustic  soda 
and  carbon  disulphide  or  its  reaction  products.  With  aqueous 
solutions  of  greater  strength  than  i  per  cent  cellulose  this  de- 
composition causes  the  formation  of  a  jelly  of  the  shape  and 
volume  of  the  containing  vessel.  This  jelly  gradually  contracts 
with  the  expulsion  of  water.  Observations  on  100  c.c.  of  a 
5  per  cent  solution  kept  in  a  stoppered  vessel  at  ordinary  temper- 
atures showed  the  following  rates  of  coagulation  and  shrinkage.1 
(See  table  on  p.  22.) 

The  cellulose  regenerated  from  viscose  differs  from  the  original 
in  being  more  hygroscopic,  as  well  as  being  hydrated,  and  in 
being  more  reactive  toward  bases  but  less  so  toward  acid  groups. 

Viscose  finds  extensive  use  in  the  manufacture  of  artificial  silk 
and  in  the  preparation  of  films  for  transparent  wrappings. 

1  Cross  and  Bevan:  Text-Book  of  Paper  Making,  3rd  ed.,  p.  25. 


22 


CELLULOSE 


These  latter  are  very  thin,  o.ooi  inch,  and  as  compared  with 
nitrate  or  acetate  films  are  much  more  water-absorbent. 


Time  in  days 

Vol.  of  cellu- 
lose hydrate 

Diff.  from  100 
c.c.  =  vol. 
expressed 

Coagulation  

8th  day 

c.c. 

c.c. 

First  appearance  of  liquid  

nth 

1  6th 

98.0 

2  .O 

20th 

83.5 

l6.S 

25th 

72.0 

28.0 

30th 

58.0 

42.O 

4oth 

42.8 

57-2 

47th 

38.5 

61.5 

The  Groups  of  Celluloses.  Up  to  this  point  the  remarks  have 
applied  chiefly  to  cotton,  which  may  be  considered  as  the  typical 
cellulose,  but  there  are  also  numerous  other  celluloses  which 
differ  more  or  less  widely  from  this  standard.  The  fibrous 
celluloses,  for  instance,  are  grouped,  according  to  C.  F.  Cross, 
into  three  classes,  depending  upon  their  degree  of  resistance  to 
hydrolytic  and  oxidizing  actions,  the  amount  of  furfural  which 
they  yield  when  boiled  with  dilute  hydrochloric  acid,  and  their 
elementary  composition  as  regards  the  ratio  of  carbon  to  oxygen. 
The  characteristics  of  the  three  groups  may  be  tabulated  as 
follows : 


A 
Cotton  group 

B 
Wood  cellulose 
group 

C 
Cereal  cellulose 
group 

Hygroscopic  moisture  
Elementary  composition 
C:O 
Furfural 

6-8% 
f  44.0-44.4 
5o 
o.i-o  4% 

9-n% 
43-0-43-5 

3-6% 

10-12% 
41.5-42.5 

12-15% 

Other  characteristics  

(No  active 
CO  groups 

Some  free  CO 
groups 

Considerable  re- 
activity of  CO 
groups 

In  group  A  are  included  cotton,  flax,  hemp,  rhea  (ramie), 
sunn  hemp,  etc.  They  are  usually  associated  in  the  plant 
world  with  substances  easily  removed  by  digestion  with  alkalis. 


COMPOUND   CELLULOSES  23 

The  purified  celluloses  of  this  group  are  considered  chemically 
identical  with  cotton. 

Group  B  comprises  celluloses  obtained  by  the  decomposition 
of  compound  celluloses,  i.e.,  those  from  woods  and  lignified 
tissues  in  general.  They  may  be  considered  as  oxidized  and 
partially  hydrolyzed  products  and  are  more  readily  attacked  by 
hydrolyzing  agents  than  are  the  celluloses  of  group  A . 

The  fibres  of  group  C  are  in  most  cases  complex,  both  struc- 
turally and  chemically.  They  are  oxycelluloses  and  are  still 
less  resistant  than  the  group  B  celluloses.  They  undergo  gradual 
oxidation  in  dry  air  at  a  temperature  of  100  degs.  and  become 
discolored. 

In  still  a  fourth  group  may  be  classed  those  cellular,  rather 
than  fibrous,  celluloses  which  offer  low  resistance  to  hydrolysis. 
These  are  easily  resolved  by  boiling  with  dilute  acids  and  are 
also  soluble  to  some  extent  in  dilute  alkaline  solutions.  As  the 
celluloses  of  this  group  are  not  employed  in  paper  making  no 
further  discussion  of  their  properties  is  essential  in  this  work. 

Compound  Celluloses.  Passing  from  the  consideration  of  the 
purified  celluloses  to  what  may  be  called  their  raw  materials,  it 
is  found  that  plant  physiologists  recognize  three  modified  or 
"compound"  celluloses:  cutocellulose,  pectocellulose  and  ligno- 
cellulose. 

Cutocelluloses  contain,  mixed  with  the  tissues,  various  oily 
and  waxy  substances  which  render  them  quite  water-resistant. 
The  two  principal  types  of  these  compound  celluloses  are  cork 
and  the  cuticular  tissues  of  leaves,  stems,  etc.  Cork  contains,  in 
addition  to  oils  and  waxes,  tannins,  lignocelluloses  and  nitroge- 
nous materials.  No  celluloses  of  this  type  are  employed  in 
paper  manufacture,  hence  a  knowledge  of  their  properties  is  only 
of  incidental  interest. 

The  pectocelluloses  may  be  considered  either  as  compounds 
or  intimate  mixtures  of  cellulose  and  colloidal  carbohydrates 
which  are  easily  hydrolyzed  by  either  acid  or  alkaline  treat- 
ments to  simpler,  soluble  materials.  They  .are  "  saturated 
compounds"  and  therefore  do  not  react  with  the  halogens.  Cel- 


24  CELLULOSE 

luloses  of  this  kind  are  widely  distributed  in  the  plant  world 
and  are  extremely  varied  in  composition  and  structural  char- 
acter. Among  the  more  important  pectocelluloses  are  flax  and 
such  other  non-lignified  fibres  as  ramie,  hemp,  nettle  fibres, 
sisal,  esparto,  bamboo,  etc.  Many  of  these  are  more  or  less 
associated  with  lignocelluloses.  While  many  of  the  pecto- 
celluloses enter  into  paper  making  operations,  it  is  not  as  pecto- 
celluloses, but  only  after  the  separation  of  the  pectic  constituents 
by  means  of  alkaline  hydrolysis. 

Lignocelluloses  form  by  far  the  most  important  group  of 
compound  celluloses,  so  far  as  paper  making  operations  are  con- 
cerned, both  because  they  are  employed  directly,  as  in  the  case 
of  ground  wood  and  jute,  and  also  because  they  are  the  basic 
raw  materials  from  which  the  greater  part  of  the  paper  making 
celluloses  are  prepared.  They  have  been  studied  in  consider- 
able detail  by  Cross  and  Bevan,  who  worked  on  jute  fibre,  which 
they  consider  to  be  the  typical  lignocellulose. 

One  essential  feature  of  lignification  is  the  formation  of  meth- 
oxyl  groups,  O  •  CH3,  while  a  second  ketonic  grouping,  CO  •  CH2, 
is  also  a  characteristic  constitutional  feature.  This  latter  group 
doubtless  plays  an  important  part  in  the  formation  of  acetic 
acid  during  hydrolysis.  Woods  are  more  pronounced  ligno- 
celluloses than  jute,  having  more  non-cellulose  constituents  and 
yielding  more  methoxyl  and  furfural.  They  are  still  further 
differentiated  from  jute  by  their  behavior  toward  cellulose  solv- 
ents, since  they  yield,  as  a  whole,  to  no  process  of  solution  and 
are,  moreover,  almost  totally  resistant  to  the  thiocarbonate 
(viscose)  reaction.  In  all  but  these  two  characteristics  the 
lignocelluloses  of  jute  and  wood  are  very  much  alike. 

Jute  lignocellulose  is  dissolved  by  cuprammonium  and  by 
zinc  chloride  either  in  aqueous  or  acid  solution.  Hydrolysis 
accompanies  the  solvent  action,  so  that  on  precipitation  the 
recovery  of  the  lignocellulose  is  incomplete. 

Alkalis  at  high  temperature  attack  and  dissolve  the  lignin 
and  the  less  resistant  cellulose  but  at  the  same  time  some  of  the 
more  resistant  cellulose  is  also  dissolved.  The  residual  cellulose, 


COMPOUND   CELLULOSES  25 

in  the  case  of  jute,  is  very  similar  in  composition  to  the  normal 
cellulose.  Acids,  even  in  dilute  solutions,  rapidly  disintegrate 
lignocelluloses  at  temperatures  above  60  degs.  Caustic  soda 
and  carbon  disulphide  dissolve  only  part  of  the  lignocellulose, 
50  to  75  per  cent  remaining  undissolved  but  in  such  a  hydrated 
and  swollen  condition  that  it  has  been  known  to  occupy  one 
hundred  times  the  volume  of  the  original  fibre.  This  insoluble 
residue  reacts  with  chlorine  as  does  the  original  fibre.  Oxidizing 
agents  profoundly  attack  lignocelluloses  with  the  formation  at 
first  of  acid  products  and  finally,  on  further  oxidation,  of  carbon 
dioxide  and  water. 

Because  of  the  difficulty  of  separating  lignin  from  cellulose 
without  causing  decomposition  or  structural  changes,  its  com- 
position is  still  regarded  as  uncertain.  Klason  1  assigns  to  lignin 
the  empirical  formula  C4oH420n  and  believes  the  evidence  goes 
to  show  that  lignin  is  not  in  chemical  union  with  the  cellulose. 
Cross  and  Bevan,2  on  the  other  hand,  have  concluded  "  that  the 
fibre  substance  is  not  merely  a  mixture  of  cellulose  with  non- 
cellulose  constituents,  but  that  these  are  compacted  together 
into  a  homogeneous  though  complex  molecule  by  bonds  of 
union  of  a  strictly  atomic  character."  They  submit  the  follow- 
ing constitutional  formula  3  for  the  lignin  (lignone)  of  the  typical 
lignocellulose,  as  representing  its  quantitative  reactions  of  chlo- 
rination,  resolution  by  bisulphites,  production  of  acetic  acid  and 
estimation  of  methoxyl. 


/C°\  /°\  /°\  /O 

HC  |CH-[CH2  .  C0]2-  HC  CH  •  CH  •  CH  •  CH/         ft  a 

HC  CO  CH3O»HC  CH.OCHs 


Lignin  has  been  investigated  by  Heuser  and  Skioldebrand4 

1  Klason:  Beitrage    zur    Kenntniss    der    chemischen     Zusammensetzung    des 
Fichtenholzes. 

2  Cross  and  Bevan:  Cellulose,  p.  134,  London,  1895. 

3  Cross  and  Bevan:  Researches  on  Cellulose,  III,  104. 

4  Heuser  and  Skioldebrand:  Z.  angew.  Chem.,  1919,  32,  41-45. 


26  CELLULOSE 

who  prepared  it  from  spruce  wood  sawdust  by  hydrolyzing 
with  42  per  cent  hydrochloric  acid.  The  yield  obtained  was 
33.12  per  cent  and  the  air  dry  lignin  contained  9.25  per  cent 
moisture  and  0.485  per  cent  ash.  It  yielded  no  furfural  but 
showed  a  copper  number  of  12.90  and  a  methyl  value  of  6.77 
per  cent.  On  destructive  distillation  it  gave  more  charcoal  and 
tar  and  less  acetic  acid  than  cotton  or  wood  cellulose. 

Lignin  shows  a  number  of  color  reactions  which  are  of  much 
value  in  detecting  the  presence  of  incrusting  matters  in  paper 
or  its  raw  materials.  Nitric  acid  gives  a  yellowish  brown  color; 
a  solution  of  aniline  sulphate  in  water  stains  lignified  tissues 
yellow;  paranitroaniline  in  hydrochloric  or  sulphuric  acid  solu- 
tion produces  a  bright  yellowish  orange  color;  while  an  alcoholic 
solution  of  phloroglucin  acidified  with  hydrochloric  acid  devel- 
ops an  intense  rose  red  or  magenta  color.  This  latter  reagent 
has  been  used  as  a  basis  for  a  quantitative  method  for  estimating 
ground  wood  in  papers.1  Schwalbe,2  however,  states  that  the  color 
reaction  with  phloroglucin  fails  in  many  cases  where  lignified  fibres 
are  present  and  considers  that  the  results  should  be  confirmed 
in  every  case  by  Cross  and  Sevan's  chlorination  reaction. 

One  of  the  most  characteristic  reactions  of  lignin  is  that  of 
direct  combination  with  the  halogens,  and  more  especially  with 
chlorine.  In  the  presence  of  water,  chlorine  attacks  lignin  with 
the  formation  of  a  chloride,  CigHisCUOg.  This  chloride  is  bright 
yellow  in  color  and  is  soluble  in  sodium  sulphite  solution  with 
the  production  of  an  intense  magenta  red  color.  With  jute  the 
chlorine  combining  with  the  lignin  amounts  to  8  per  cent  of 
the  lignocellulose  and  an  equal  amount  is  combined  as  hydro- 
chloric acid;  with  wood,  on  the  other  hand,  the  proportions  are 
not  equal,  considerably  more  chlorine  going  to  form  hydro- 
chloric acid  than  corresponds  with  that  which  is  used  in  chlo- 
rinating the  lignin.  This  reaction  with  chlorine  is  simple  and 
there  is  no  indirect  oxidation  as  a  result  of  the  reaction  C12  +  H2O 
=  2  HC1  +  O.  The  chlorinated  material  is  homogeneous  and  as 

1  Cross,  Bevan  and  Briggs:  Chem.  Ztg.,  1907,  31,  725. 

2  Schwalbe:  Z.  angew.  Chem.,  1918,  31,  pp.  50  and  57. 


DETERMINATION  OF   CELLULOSE  27 

the  cellulose  is  unattacked,  maximum  yields  of  the  latter  are 
obtained.  This  reaction  forms  the  basis  of  Cross  and  Bevan's 
method  for  the  quantitative  determination  of  cellulose. 

Determination  of  Cellulose.  The  amount  of  cellulose  in  any 
raw  material  determines  the  maximum  yield  of  pure  fibre  which 
can  be  prepared  by  any  of  the  chemical  processes  used  in  pulp 
making.  Practically,  however,  the  yield  never  reaches  this  the- 
oretical maximum  because  of  the  hydrolytic  action  of  the  cook- 
ing liquors  and  the  oxidizing  and  solvent  action  of  the  alkaline 
bleaching  agents  used.  A  method  for  accurately  determining 
the  cellulose  in  wood,  or  any  fibrous  raw  material,  is  therefore 
of  great  value  to  the  paper  maker,  in  that  it  enables  him,  on  the 
one  hand,  to  detect  variations  in  his  supplies  and,  on  the  other,  to 
see  how  nearly  his  processes  are  approaching  the  optimum. 

A  satisfactory  method  for  the  determination  of  cellulose 'must 
separate  it  in  a  form  which  is  free  from  lignin  and  colored  im- 
purities and  which  is  as  pure  as  possible.  Freedom  from  min- 
eral matter  is  of  secondary  importance  since  it  can  be  allowed 
for  or  removed  by  treatment  with  dilute  acids.  The  formation 
of  oxycellulose  and  hydrocellulose  must  especially  be  guarded 
against  since  in  their  formation  part  of  the  cellulose  is  converted 
to  soluble  products  and  moreover  they  are  easily  attacked  by 
many  of  the  reagents  employed.  Another  consideration  is  that 
the  process  should  involve  no  very  complicated  operations  and 
that  it  should  be  capable  of  completion  within  a  reasonably 
short  time. 

Many  methods  for  determining  cellulose  have  been  proposed, 
of  which  some  do  not  remove  all  non-cellulose  matter,  some 
destroy  part  of  the  cellulose  itself,  and  some,  which  give  pure 
products,  are  too  long  and  complicated  for  practical  work.  It 
is  unnecessary  to  give  the  full  details  of  all  the  proposed  methods, 
but  a  very  brief  description  may  prove  of  interest  to  those  who 
wish  to  study  into  the  subject.  The  following  outlines,  to- 
gether with  notes  on  the  purity  of  the  products,  are  taken  from 
Renker's  1  work  on  methods  of  determining  cellulose. 

1  Ranker:  Uber  Bestimmungsmethoden  der  Cellulose,  Berlin,  1910. 


28  CELLULOSE 

Konig 1  heats  3  grams  of  the  sample  with  200  c.c.  of  glycerine 
(sp.  gr.  1.230)  and  4  grams  of  concentrated  sulphuric  acid.  The 
flask  is  fitted  with  a  reflux  condenser  and  the  heating  is  con- 
tinued for  just  one  hour  at  the  boil  (131  to  133  degs.);  the 
residue  is  then  washed  with  hot  water,  alcohol  and  ether,  dried 
and  weighed.  This  process  strongly  attacks  the  cellulose  and 
the  product  is  not  pure  cellulose  though  entirely  free  from 
pentosans. 

Cross  and  Bevan's2  method  depends  upon  the  chlorination 
of  the  lignin  by  treating  the  moist  material  with  chlorine  gas 
and  the  subsequent  solution  of  the  chlorinated  products  by 
boiling  with  dilute  sodium  sulphite  solution.  The  cellulose  ob- 
tained is  pure  white  and  free  from  lignin,  but  consists,  according 
to  the  terminology  of  Cross  and  Bevan,  of  a  mixture  of  a  and  /3 
celluloses,  the  latter  being  of  low  resistance  toward  hydrolytic 
agents  and  yielding  furfural  on  boiling  with  hydrochloric  acid. 

Modifications  of  Cross  and  Bevan's  method  in  which  chlorine 
water  is  used  instead  of  the  gas  give  lower  yields  and  the  product 
contains  some  oxy cellulose. 

In  H.  Muller's 3  process  the  sample,  after  extraction  of  the 
resins  and  boiling  in  water,  is  treated  with  5  to  10  c.c.  of  dilute 
bromine  water  diluted  with  100  c.c.  of  water.  When  the  color 
indicates  that  the  bromine  is  all  used  up,  more  bromine  water 
is  added  until  an  excess  of  the  reagent  remains;  this  takes  from 
12  to  24  hours.  The  residue  is  filtered  off  and  washed.  This 
process  is  repeated  until  the  fibrous  residue  is  pure  white.  This 
process  yields  highly  pure  cellulose  which  is  free  from  oxycel- 
lulose  but  too  long  a  time  is  required,  especially  with  woods 
which  may  require  twenty  repetitions  of  the  treatment.  Kla- 
son's4  modification,  involving  preliminary  treatment  of  the 
sample  with  calcium  or  magnesium  bisulphite  solution,  gives 
lower  yields  than  Muller's  original  method  and,  although  the 


1  Konig:  Z.  Nahr.  Genussm.,  i,  8 

2  Cross  and  Bevan:  Cellulose,  95  (1895). 

3  Hofmanns  Ber.  iiber  die  Entwickl.  d.  chem.  Industrie,  III,  27  (1877). 

4  5  Internationaler  Kongress  fiir  angewandte  Chemie,  1903, 1,  309. 


DETERMINATION  OF   CELLULOSE  29 

time  required  is  less,  the  method  is  still  unsatisfactory  tech- 
nically. 

The  Schulze-Henneberg 1  method  consists  in  digesting  the 
sample  for  12  to  14  days  at  15°  C.  with  0.8  part  KC1O3  and  12 
parts  HN03  (i.io  sp.  gr.).  This  is  followed  by  dilution,  filter- 
ing and  washing  and  then  by  digestion  with  dilute  ammonia  for 
45  minutes  at  60°  C.  The  residue  is  washed  with  ammonia  and 
finally  hot  water.  This  process  requires  an  excessive  time  and 
very  careful  control  of  the  temperature,  and  the  results  obtained 
are  low  and  irregular,  especially  with  woods. 

Hoffmeister 2  treats  the  sample  with  hydrochloric  acid  (1.05 
sp.  gr.)  and  as  much  potassium  chlorate  as  will  dissolve  during 
the  reaction.  The  digestion  is  conducted  at  ordinary  tempera- 
ture,—  not  over  17.5°  C., —  with  frequent  shaking  for  24  to  36 
hours  or  until  all  parts  of  the  fibre  have  become  a  clear  yellow. 
The  residue  is  then  washed,  digested  on  the  water  bath  for  i  to  2 
hours  with  dilute  ammonia,  washed,  dried  and  weighed.  This 
process  yields  a  product  which  is  free  from  lignin  but  is  some- 
what yellow;  the  cellulose  is  somewhat  attacked  and  oxycellu- 
lose  is  present. 

Digestion  at  60  degs.  with  a  large  excess  of  nitric  acid  (10 
per  cent)  has  been  proposed  by  Cross  and  Bevan.3  When  the 
fibre  has  changed  to  a  yellow  color  it  is  washed  and  treated 
with  a  solution  of  sodium  sulphite.  This  treatment  hydrolyzes 
and  dissolves  the  0  cellulose  and  leaves  only  the  more  resistant 
a  cellulose;  this  results  in  low  yields  as  compared  with  the 
chlorination  process.  The  products  are  free  from  lignin  but 
contain  oxycellulose  and  apparently  also  hydrocellulose. 

Lifschlitz 4  digests  the  material  for  14  to  16  hours  at  a  tem- 
perature of  45  to  60  degs.  with  10  parts  of  a  mixture  of  32  per  cent 
sulphuric  acid,  1 8  to  20  per  cent  nitric  acid  and  48  to  50  per  cent 
water.  With  wood,  very  low  yields  are  obtained  and  the  prod- 

1  Ann.,  146,  130  (1868). 

2  Landw.  Jahrb.,  17,  240  (i 

3  Cellulose,  97  (1895). 

4  Ber.,  24,  1188  (1891). 


30  CELLULOSE 

uct  forms  a  brownish  horny  mass  which  is  free  from  lignin  but 
contains  considerable  oxycellulose. 

Schwalbe1  treats  the  moist  material  for  several  hours  with 
gases  containing  oxides  of  nitrogen,  washes  and  heats  on  the 
water  bath  with  a  2  per  cent  Na2SO3  solution.  The  cellulose 
thus  obtained  is  free  from  lignin  but  contains  oxidation  products 
and  is  brownish  yellow.  The  results  are  very  variable  when 
woods  are  analyzed. 

Zeisel  and  Stritar2  suspend  the  sample  in  dilute  nitric  acid 
and  add  a  3  per  cent  solution  of  potassium  permanganate  a 
cubic  centimeter  at  a  time  until  the  color  persists  for  half  an 
hour;  during  this  treatment  cooling  and  stirring  are  necessary. 
The  manganese  salts  are  removed  by  S02-water  or  NaHS03 
and  after  washing  the  residue  is  digested  with  dilute  ammonia. 
It  is  claimed  that  hemicelluloses  and  about  4  per  cent  of  the 
cellulose  are  dissolved.  The  method  gives  low  and  variable 
results,  forms  much  oxycellulose  and  is  unsatisfactory  for  woods. 

Neutral  permanganate  does  not  remove  all  the  lignin,  while 
if  it  is  used  with  acetic  acid  the  product  is  free  from  lignin  but 
contains  oxycellulose.  Permanganate  with  hydrochloric  acid 
works  fairly  well  with  cotton,  jute  and  sulphite,  but  with  woods 
the  treatment  must  be  many  times  repeated  and  the  results 
are  low. 

Sodium  hypochlorite  was  found  to  give  low  results  and  though 
the  product  was  free  from  lignin  it  was  very  high  in  oxycellulose.3 

After  a  large  number  of  experiments  with  the  different  meth- 
ods, Renker  concludes  that  there  is  no  absolutely  correct  method 
for  determining  cellulose  but  that  the  method  of  Cross  and 
Bevan  using  chlorine  gas  is  the  most  satisfactory.  Konig  and 
Huhn,4  on  the  contrary,  contend  that  Cross  and  Bevan's  method 
gives  too  high  results  because  it  fails  to  remove  pentosans  and 
hemicelluloses  which  remain  as  impurities  in  the  product.  They 

1  D.R.P.,  204,460. 

2  Ber.,  35,  1252  (1902). 

3  Renker:  Bestimmungsmethoden  der  Cellulose,  79. 

4  Z.  Farben-Ind.,  1911,  n,  297  et  seq. 


DETERMINATION  OF  CELLULOSE 


claim  that  only  hydrolysis  followed  by  oxidation  can  free  the 
true  cellulose  from  all  impurities.  This  brings  up  the  question 
of  what  constitutes  pure  cellulose,  which  has  never  been  settled 
beyond  dispute  and  about  which  there  are  probably  as  many 
opinions  as  there  are  methods  for  its  determination. 

The  results  obtained  by  Renker,  in  his  investigation  of  the 
different  methods  for  the  determination  of  cellulose,  are  given  in 
the  accompanying  table.  The  percentages  are  based  on  mate- 
rial free  from  ash,  fat  or  rosin,  and  water-soluble  substances. 


Method  of  analysis 

Material 

Sulphite 
cellulose 

Jute 

Wood 

Cotton 

Glycerine-sulphuric  acid.  —  Konig 

Per  cent 

74-15 
97-9 
97.65 
98.0 
98-1 
96.6 

98-05 

98-25 
97.65 
98.2 

90.6 
98.5* 
98.25 

97-9 
96-05 

97-4 
90.75 

Per  cent 

Per  cent 

Per  cent 

Chlorine  gas  —  Cross  and  Bevan 

84.5 
83.4 
81.1 

83-3 
80.8 

79-2 

82.5 
79-75 
80.65 

70.95 
87.4* 
83.6 

82.9 

83-4 
79-4 

60.55 
57-1 

57-95 
51-85 

58.1 

57-15 
53-6 
55-8 
43-35 

40.2* 

43-o 

50.5 
Si-9 

97-85 
94-7 
96.8 

97-1 
95-45 

96.95 

96.15 
96.35 
98.85 

93-25 
97-6 

96-65 
96.55 
96.8 
94-2 

Concentrated  chlorine  water.  .  .        .        .... 

Dilute  chlorine  water  

Bromine  water.  —  H.  Miiller  
Bromine  water.  —  Miiller-Klason  
Nitric    acid    and    potassium    chlorate.  — 
Schulze  

Muriatic   acid  and  potassium  chlorate.  — 
Hoffmeister. 

Nitric  acid  —  Cross  and  Bevan  . 

Nitrous  acid.  —  German  pat.  204,460  
Nitric-sulphuric  acicls.  —  Lifschiitz  
Potassium  permanganate  and  nitric  acid.  — 
Zeisel  and  Stritar 

Potassium  permanganate,  neutral  
Potassium  permanganate  and  acetic  acid  .  .  . 
Potassium  permanganate  and  hydrochloric 
acid                                                                  •  • 

Hydrogen,  peroxide         .         

Sodium  hypochlorite  .  .               

Phenol  —  German  pat.  94,467  

*  Inapplicable  because  lignin  is  not  all  removed. 

All  things  considered  the  Cross  and  Bevan  method,  employing 
chlorine  gas,  is  doubtless  the  best  means  of  determining  cellu- 
lose, especially  where  woods  are  under  consideration,  since  it 
has  been  proved  by  Heuser  and  Sieber  1  that  lignin  can  be  com- 
pletely removed  by  chlorination  without  any  oxidation  of  the 

1  Z.  angew.  Chem.,  26  (1913),  801. 


32  CELLULOSE 

cellulose,  and  because  the  color  produced  by  sodium  sulphite  on 
chlorinated  lignin  is  characteristic  and  forms  a  good  indicator 
to  show  the  degree  of  purification.  If,  however,  the  chlorine  is 
allowed  to  act  after  the  lignin  is  all  removed  the  cellulose  is 
gradually  converted  to  oxycellulose,  which  is  soluble  in  sodium 
sulphite,  and  lower  yields  result.  According  to  one's  under- 
standing of  pure  cellulose  it  may  or  may  not  be  advisable  to 
accompany  this  treatment  with  one  of  acid  hydrolysis. 

Even  where  Cross  and  Bevan's  method  has  been  employed  the 
different  methods  of  operation  render  the  figures  of  different 
observers  hardly  comparable.  The  wood  must  be  very  finely 
divided  and  of  uniform  particles.  If  coarse  pieces  are  present 
the  lignin  chloride  formed  on  the  surface  prevents  further  pene- 
tration of  the  gas  and  long  exposure  is  of  little  use  unless  the 
lignin  chloride  is  removed.  Variation  in  the  size  of  the  wood 
particles  also  means  that  a  portion  will  be  over-treated  in  order 
to  insure  the  complete  removal  of  the  lignin  from  the  rest,  and 
this  results  in  lower  yields.  To  avoid  many  of  the  manipula- 
tive variations  Johnsen  and  Hovey  1  worked  on  wood  reduced 
to  a  fine  "sawdust"  by  rasping  with  a  suitable  wood  rasp,  and 
screened  to  pass  an  8o-mesh  but  not  a  loo-mesh  sieve.  This 
they  chlorinated  in  a  Gooch  crucible,  the  small  plate  of  which 
was  carefully  covered  with  fine  bleached  cloth  sewn  on  with 
cotton  thread.  Their  method,  which  includes  a  preliminary 
hydrolysis,  is  in  detail  as  follows: 

Two  samples  of  about  one  gram  each  of  air  dry  sawdust  are 
weighed  exactly,  transferred  to  small  flasks  and  heated  for  one- 
half  hour  with  alcohol,  on  a  water  bath,  filtered  through  the 
crucibles  and  washed  with  hot  alcohol.  The  material  is  then 
transferred  from  the  crucibles  to  150  c.c.  flasks  and  covered 
with  about  75  c.c.  of  glycerine-acetic  acid  mixture  (60  grams 
glacial  acetic  acid  and  92  grams  glycerine,  1.26  sp.  gr.).  The 
flasks  are  then  heated  in  an  oil  bath  at  135°  C.  for  four  hours, 
using  glass  tubes  as  reflux  air  condensers.  The  material  is  then 
collected  in  the  crucibles,  washed  well  with  hot  water  and  the 

1  Pulp  and  Paper  Mag.  Can.,  XVI  (1918),  85. 


DETERMINATION  OF   CELLULOSE  33 

crucibles,  after  cooling,  are  placed  in  an  apparatus  permitting 
washed  chlorine  gas  to  be  passed  directly  through  the  crucible 
and  its  contents.  After  passing  chlorine  through  continuously 
for  20  minutes  the  free  gas  is  removed  by  washing  once  with  a 
cold,  weak  solution  of  sulphurous  acid  in  water,  and  the  cru- 
cibles are  placed  in  small  beakers  which  are  filled  not  quite  to 
the  top  of  the  crucibles  with  a  3  per  cent  solution  of  sodium 
sulphite.  After  the  beakers  have  been  heated  in  a  water  bath 
for  three-quarters  of  an  hour  the  material  in  the  crucibles  is 
washed  with  hot  water,  using  a  filtering  flask,  and  allowed  to 
cool.  The  chlorination  process  is  then  repeated  three  times 
exactly  as  before  except  that  the  duration  of  gassing  is  15,  15 
and  10  minutes.  After  the  last  treatment  with  sodium  sulphite 
the  fibres  are  thoroughly  washed,  dried 'at  105°  C.  for  four 
hours,  or  to  constant  weight,  and  weighed  in  closed  weighing 
bottles.  The  moisture  in  a  separate  sample  of  the  original 
sawdust  having  been  determined,  the  per  cent  of  cellulose  can 
be  calculated  over  to  the  basis  of  bone  dry  wood. 

Working  by  this  method  the  lignin  may  be  completely  re- 
moved from  finely  divided  wood  in  four  chlorinations  totalling 
one  hour's  exposure  to  the  gas.  If  the  treatment  with  glycer- 
ine and  acetic  acid  is  omitted  the  results  are  2  to  4  per  cent 
higher,  indicating  the  extent  to  which  hydrolysis  removes  sub- 
stances which  are  not  dissolved  by  the  straight  chlorination 
process. 


CHAPTER  H 
FIBROUS   RAW  MATERIALS 

The  Vegetable  Cell.  The  structural  unit  of  which  the  plant 
fabric  is  composed  is  the  cell,  and  even  those  elements  which 
are  least  cellular  in  appearance,  as  fibres,  ducts,  etc.,  are  only 
transformed  cells,  or  simple  combinations  of  them.  In  all  of 
the  higher  forms  of  plant  life  the  living  cell  consists  essentially 
of  protoplasm  surrounded  by  a  wall  of  cellulose.  The  proto- 
plasm is  practically  transparent  and  colorless  but  it  is  seldom 
found  without  an  admixture  of  other  matter  which  gives  it  a 
granular  appearance.  Chemically  considered  it  is  a  very  com- 
plex substance  belonging  to  the  group  of  albuminoid  bodies 
and  is  quite  similar  in  composition  and  appearance  to  the  albu- 
min which  forms  white  of  egg. 

The  cell  wall  is  produced  from  the  substances  contained  in 
the  protoplasm  and  is  formed  in  close  contact  with  the  limiting 
film  of  the  latter.  At  first  it  is  an  even,  homogeneous  film 
showing  no  obvious  structure  but  it  soon  becomes  modified  in 
appearance  and  composition  according  to  its  location  in  the 
plant;  in  some  cases  it  becomes  capable  of  absorbing  a  large 
amount  of  water  with  a  consequent  increase  in  volume  and  the 
formation,  upon  warming,  of  a  thick  mucilage.  In  other  cases 
it  becomes  mineralized  by  the  deposition  of  silica  or  calcium 
salts  upon  or  within  the  cell  wall,  the  effect  being  a  hardening 
and  stiffening  of  the  structure  as  illustrated  by  many  of  the 
grasses  and  straws.  A  third  modification  of  the  cell  wall  is 
known  as  cutinization  or  suberification.  Ordinary  cell  walls 
absorb  water  freely  but  in  certain  parts  of  the  plant  they  are 
water-repellent  due  to  the  presence  of  cutin  or  suberin.  This 
water-proofing  of  the  cell  wall  may  be  superficial  only  or  it  may 
permeate  the  entire  structure  of  the  wall  as  in  the  case  of  cork. 

34 


THE  VEGETABLE   CELL 


35 


A  fourth  change,  which,  from  the  point  of  view  of  the  paper 
maker,  is  far  more  important  than  the  others,  is  known  as  ligni- 
fication  and  is  caused  by  the  deposition  in  and  upon  the  cell- 
wall  of  a  substance  somewhat  similar  to  cellulose  and  which  is 
termed  lignin.  This  material,  although  generally  spoken  of  as 
a  single  substance,  is  in  all  probability  made  up  of  several 
closely  related  substances.  It  forms  by  far  the  greater  part  of 
the  incrusting  matters  which  are  removed  by  the  treatment 
with  chemicals  in  preparing  celluloses  for  paper  making.  The 
chemical  properties  of  the  lignocelluloses  have  already  been 
described  in  the  preceding  chapter. 

The  thickening  of  the  cell  wall,  which  up  to  a  certain  age 
accompanies  the  deposition  of  lignin,  seldom  takes  place  uni- 
formly over  its  entire  surface.  As  a  result  the  fibres  may  show 
ridges,  depressions,  pits,  rings,  spirals  and  other  markings,,  which 
are  often  so  characteristic  as  to  be  of  great  assistance  in  the 
identification  of  the  fibres  in  which  they  occur.  In  some  cases 
it  is  easy  to  see  that  the  markings  are  pores  or  fissures  running 
from  one  cell  to  the  next.  Such  pores  and  the  thinner  portions 
of  the  cell  walls  aid  in  the  transmission  of  sap. 

In  many  plants  gums  and  resins  are  formed  by  processes 
which  are  not  well  understood  but  which  are  probably  in  large 
part  degradations  of  the  cell  walls.  The  products  of  such 
changes  are  often  found  as  small,  irregular  drops  either  within 
the  cells  or  in  the  spaces,  known  as  resin  ducts,  arising  from  the 
confluence  of  a  number  of  cells.  The  resins  are  soluble  in  alco- 
hol or  in  solutions  of  the  alkalis;  they  are  colored  reddish  orange 
by  a  solution  of  Sudan  III  in  diluted  alcohol  and  when  stained 
in  this  way  may  be  readily  recognized  under  the  microscope. 

It  is  only  the  living  cells  which  contain  protoplasm  and  these 
are  found  at  the  points  where  growth  is  taking  place.  The  older 
cells,  where  growth  has  ceased,  occasionally  contain  a  little 
water  but  generally  only  air,  more  or  less  highly  rarefied.  They 
are  still  of  value  in  the  plant  structure  for  it  is  from  such  lifeless 
cells  that  stiffness  and  strength  are  derived.  Cells  are  present 
in  different  -plants  in  an  almost  infinite  diversity  of  form,  but, 


36  FIBROUS  RAW  MATERIALS 

except  for  those  cases  which  assist  in  the  identification  of  the 
fibres  which  they  accompany,  the  following  discussions  will  be 
confined  to  the  long,  slender  pointed  elements  of  the  bast  or 
woody  tissues,  which,  with  the  single  exception  of  cotton,  are 
the  only  ones  of  practical  interest  to  the  paper  maker.  Such 
fibres  are  derived  from  the  ordinary  cells  simply  by  growth  and 
change  of  form. 

The  paper  making  fibres  may  be  divided,  according  to  their 
source,  into  four  classes. 

1.  Seed  hairs,  of  which  cotton  is  the  only  representative. 

2.  Bast  fibres,  as  hemp,  flax,  manila,  etc. 

3.  Those  derived  from  whole  stems,  such  as  straw,  esparto, 
or  bamboo,  and  which  are  associated  with  various  cells  and 
vessels  which  are  not  properly  fibres. 

4.  Fibres  derived  from  wood. 

Seed  Hairs 

Cotton  (Gossypium).  The  cotton  fibre  consists  of  a  single 
hair-like  cell,  which  when  fully  ripe  is  flattened  and  twisted. 
This  appearance  is  a  characteristic  of  fully  matured  cotton  and 
is  not  shown  by  unripe  fibre  or  that  which  has  been  injured 
during  growth.  The  fibres  form  the  covering  of  the  cotton 
seed  and  are  removed  from  the  seed  by  ginning.  The  length  of 
the  cotton  fibre  varies  from  2  to  5.6  cm.  and  the  diameter 
from  0.0163  to  0.0215  mm.;  the  longest  fibres  are  found 
in  the  Sea  Island  cottons,  followed  by  Egyptian,  Brazilian, 
American  and  East  Indian.  The  cell  walls  of  the  mature  cotton 
are  thin  and  often  present  a  granulated  appearance,  or  highly 
characteristic  cross-markings. 

Raw  cotton  has  been  examined  by  Schunck  who  found  in  it 
two  coloring  matters,  both  containing  nitrogen;  a  wax  similar 
to  carnauba  wax;  albuminous  matter  and  a  solid  crystalline 
fatty  acid.  Muller  has  analyzed  raw  cotton  with  the  following 
results: 


LINEN  37 

Per  cent 

Water 7.  oo 

Cellulose 91. 35 

Fat 0.40 

Aqueous  extract  (containing  nitrogeneous  substances) o.  50 

Ash o.  12 

Cuticular  substance  (by  difference) o.  63 

Cotton  reaches  the  paper  mill  in  the  form  of  rags  and  spinning 
waste.  The  short  fibres  removed  from  the  seed  hulls  by  me- 
chanical processes  are  also  occasionally  available  and  can  be 
used  in  high-class  papers. 

Bast  Fibres 

Under  this  heading  are  included  the  fibres  found  in  the  inner 
bark  of  various  plants.  These  are  often  present  in  the  plant 
in  the  form  of  bundles  of  considerable  length  and  it  is  these 
fibre  bundles  or  filaments  which  are  of  particular  interest  in 
textile  work,  while  the  paper  maker  is  concerned  only  with  the 
ultimate  fibres  composing  these  filaments.  The  fibres  are  usu- 
ally firmly  attached  to  those  above  and  below  them,  either  by 
incrusting  matters  or  by  partial  identity  of  their  cell  walls,  so 
that  a  chemical  treatment  is  generally  necessary  in  separating 
them.  The  filaments,  on  the  other  hand,  are  isolated  from  the 
surrounding  tissues  by  various  mechanical  or  chemical  processes, 
one  of  the  commonest  being  retting  as  applied  to  flax  and  hemp. 

The  walls  of  bast  fibres  are  usually  of  considerable  thickness 
and  the  central  canal  varies  greatly  in  the  different  species 
and  even  in  different  individuals  of  the  same  species.  The 
irregularities  of  the  cell  walls  are  such  as  to  cause  thickenings 
or  knots  in  some  cases,  projections  into  the  cell  cavity  or  out- 
ward from  the  walls,  and  various  other  characteristic  appear- 
ances. Variations  in  the  amount  of  lignification  and  in  the 
nature  of  the  materials  deposited  in  and  on  the  cell  walls  are 
frequently  sufficiently  characteristic  to  assist  materially  in  their 
identification. 

Linen.  Linen  is  composed  of  the  bast  fibres  of  the  flax  plant 
Linum  usitatissimum.  The  plant  yields  about  8  per  cent  of 


FIBROUS   RAW  MATERIALS 


fibre  which  is  separated  by  retting  and  is  then  known  as  flax. 
The  ultimate  fibres  are  6  to  60  mm.  long  and  0.012  to  0.026  mm. 
wide  with  an  average  ratio  of  length  to  width  of  about  1200. 
They  are  thick  walled  tubes  with  thickened  places  or  knots  at 
intervals.  The  ends  are  tapered,  the  walls  rather  transparent, 
and  the  canal  is  small.  Mliller  gives  the  analyses  of  two  samples 
of  Belgian  flax  as  follows: 


Per  cent 

Per  cent 

Water. 

8  60 

10   ^6 

Cellulose  .  . 

81   QQ 

70  <;<> 

Fat  and  wax                                  

2  .  37 

2  .34 

Aqueous  extract  
Ash 

« 

3-62 

O    7O 

5-94 

I    32 

Pectous  substances  

2  .72 

9.29 

Linen  or  flax  reaches  the  paper  mill  in  the  form  of  scutching 
refuse,  spinning  waste,  threads,  rags,  etc.  It  requires  much 
the  same  treatment  as  given  to  cotton  except  that  it  is  necessary 
to  employ  a  rather  more  severe  bleaching  process. 

Hemp  (Cannabis  saliva).  The  fibre  is  prepared  by  retting, 
from  filaments  which  run  the  entire  length  of  the  stem.  The 
ultimate  fibres  composing  these  filaments  vary  from  5  to  55 
mm.  and  average  about  22  mm.  long  by  0.022  mm.  in  diam- 
eter, the  ratio  of  length  to  diameter  being  therefore  about  1000. 
The  fibres  have  very  thick  walls  which  are  not  very  highly 
lignified.  The  ends  are  large  and  sometimes  flattened  and  the 
central  canal  is  almost  obliterated.  In  microscopic  appearance 
the  fibres  are  very  similar  to  those  of  flax;  they  show  the  same 
knots  or  thickenings  and  the  same  striae,  but  they  differ  from 
linen  in  having  more  ability  to  break  down  into  fibrillae  during 
the  mechanical  processes  of  paper  making. 

Miiller  gives  the  following  as  the  analysis  of  a  sample  of  raw 
Italian  hemp. 

Per  cent 

Water - '. 8.80 

Cellulose 77-13 

Fat  and  Wax 0.55 


JUTE  39 

Per  cent 

Aqueous  extract 3. 45 

Ash o.  82 

Pectous  substances 9-25 

Many  other  plants  yield  fibres  to  which  the  name  hemp  is 
given  but  they  are  generally  distinguished  as  manila  hemp, 
sisal  hemp,  sunn  hemp,  etc. 

[_Hemp  comes  to  the  paper  mill  in  the  shape  of  rags,  rope  and 
cordage,  etc.  It  is  used  in  high-grade  papers,  particularly  very 
thin  sorts,  where  its  ability  to  split  into  fibrillae  makes  it  espe- 
cially valuable. 

Manila  Hemp  (Musa  textilis).  Manila  is  prepared  from  the 
outer  sheath  of  the  stems  of  the  Musa,  which  is  a  species  of 
banana,  by  stripping,  scraping  and  drying.  It  is  sometimes 
further  purified  by  washing  and  beating. 

The  ultimate  fibres  are  from  3  to  12  mm.  long  and  average 
about  6  mm.;  the  width  varies  from  0.016  to  0.032  mm.  with 
an  average  of  0.024  mm.  The  fibres  taper  very  gradually 
toward  the  ends;  the  central  canal  is  large  and  very  prominent, 
while  fine  cross-markings  are  numerous. 

The  composition  of  raw  manila  is  given  by  Muller  as  follows: 

Per  cent 

Water n.  73 

Cellulose 64. 07 

Fat  and  wax o.  62 

Aqueous  extract o.  96 

Ash i .  02 

Lignin  and  pectous  substances 21. 60 

The  paper  maker  obtains  manila  fibre  almost  entirely  in  the 
form  of  old  ropes  and  cordage.  It  is  generally  given  a  compara- 
tively light  alkaline  treatment  with  lime  and  used  in  the  un- 
bleached condition  for  papers  where  strength  is  of  far  more 
importance  than  cleanliness  or  color.  It  is  occasionally  bleached 
to  a  light  yellowish  shade  for  some  grades  of  paper. 

Jute  (Cor chorus  capsularis  and  C.  olitorius).  The  filaments 
are  obtained  by  a  retting  process,  and  are  used  in  the  manu- 
facture of  twine,  cordage,  and  woven  goods  such  as  burlap. 


FIBROUS  RAW  MATERIALS 


It  is  in  these  forms  and  also  as  " butts"  and  "rejections"  that 
it  reaches  the  paper  maker. 

The  fibres  of  jute  are  about  2  mm.  long  and  0.022  mm.  in 
diameter.  They  are  thick-walled  and  the  central  canal  is  very 
variable,  at  times  being  of  considerable  width  and  then  narrow- 
ing to  hardly  more  than  a  line.  The  surface  is  quite  smooth 
and  at  intervals  may  be  noticed  radial  canals  and  joints  similar 
to  those  in  linen  though  not  so  pronounced.  As  used  in  paper 
making  the  fibres  are  not  completely  separated,  so  that  bundles 
of  fibres  are  of  frequent  occurrence. 

Jute  has  been  carefully  studied  by  Cross  and  Bevan  who  regard 
it  as  typical  of  lignified  fibres.  They  consider  it  as  a  chemical 
unity,  which  they  term  lignocellulose,  and  which  splits  up  into 
cellulose  and  other  products  on  treatment  with  suitable  reagents. 

Miiller  gives  the  composition  of  the  raw  fibre  as  follows: 


First  quality 

Butts 

Water 

Per  cent 
9  86 

Per  cent 

12    4O 

Cellulose 

63   76 

60    89 

Fat  and  wax  

0.^8 

o  .44 

Aqueous  extract  

1  .00 

3.89 

Ash 

o  68 

I    40 

Lignin  or  non-cellulose  

24.32 

20.98 

Adansonia  (Adansonia  digitata).  This  fibre,  which  is  derived 
from  the  inner  bark  of  the  baobab,  or  monkey  bread  tree,  of 
Africa,  has  been  used  to  some  extent  in  preparing  papers  where 
the  very  highest  strength  is  a  necessity.  The  composition  of 
the  bast  as  exported  varies,  as  shown  below: l 


Per  cent 

Per  cent 

Water              

10.90 

13.18 

Cellulose  

49  .35 

58.82 

Fat  and  wax  

0.94 

0.41 

Aqueous  extract 

17  .  C7 

7.08 

Ash 

6.19 

4.72 

Pectous  substances 

19.05 

15  .19 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  128. 


FIBRES   DERIVED   FROM  .WHOLE  STEMS  41 

Paper  Mulberry  Tree  (Broussonetia  papyri/era).  The  fibres 
of  the  paper  mulberry  are  used  by  the  Japanese  in  the  prepara- 
tion of  some  of  their  peculiar  papers.  They  are  separated 
from  the  inner  bark  of  the  tree  by  scraping,  soaking  and  mace- 
ration in  water,  and  are  sometimes  purified  still  further  b.y 
boiling  in  weak  alkaline  solutions.  As  used  in  Japanese  papers 
the  fibres  are  generally  unbroken. 

The  fibres  are  long  and  slender,  varying  in  length  from  6  to 
20  mm.,  with  an  average  width  of  0.030  mm.  They  are  nearly 
transparent  when  viewed  under  the  microscope,  and  show  trans- 
verse jointings  as  well  as  longitudinal  striae.  The  central  canal 
generally  shows  as  a  well-defined  line  and  the  ends  are  some- 
times blunt  and  rounded,  sometimes  fringed. 

Agave.  Fibres  are  prepared  from  the  leaves  of  various  species 
of  agave  by  maceration  or  scraping.  The  filaments  thus  obtained 
are  light  colored,  lustrous  and  comparatively  stiff.  Among  the 
most  common  of  the  fibres  of  this  class  is  sisal  hemp  or  heniquen, 
which  is  largely  employed  for  cordage,  bags,  etc.,  in  which 
forms  it  reaches  the  paper  mill. 

The  ultimate  fibres  are  long,  of  rather  small  diameter,  taper- 
ing and  pointed  at  the  ends.  The  central  canal  is  not  promi- 
nent but  can  be  seen  as  a  narrow  line  in  some  of  the  fibres.  The 
walls  are  thick  and  are  characterized  by  many  fine  cross  lines, 
close  together,  which  are  found  on  nearly  every  specimen.  The 
fibres  are  harsher  than  paper  mulberry  and  longer  than  manila. 

Fibres  Derived  from  Whole  Stems 

The  fibres  in  this  class,  being  produced  by  treatment  of  the 
entire  stems,  include  the  ultimate  fibres  from  all  structural  ele- 
ments of  the  stem  proper,  together  with  cells  from  the  epidermis 
and  other  parts  of  the  plant. 

Straw.  In  straw  pulp  the  bast  cells  or  fibres  form  the  greater 
part  of  the  pulp.  These  are  comparatively  short  and  slender 
with  sharp  pointed  ends;  at  quite  regular  intervals  the  walls 
appear  to  be  thickened  and  drawn  together  to  resemble  joints. 


FIBROUS   RAW  MATERIALS 


The  dimensions  of  straw  fibres  vary  with  the  kind  of  straw  and 
with  the  conditions  of  growth,  nature  of  soil,  etc.  [They  are 
longer  than  those  from  esparto  but  not  so  long  as  the  fibres 
from  spruce  wood  and  would  compare  more  nearly  with  poplar 
fibre  in  paper  making  value.  J 

Accompanying  the  bast  fibres  in  straw  pulp  are  numerous 
epidermal  cells  with  toothed  or  serrated  edges,  and  also  smooth, 
thin-walled  cells  from  the  pithy  portion  of  the  stem.  The 
latter  vary  in  shape  from  nearly  round  to  long,  oval  cells  whose 
length  is  several  times  their  width.  Both  types  of  cell  aid 
materially  in  the  identification  of  straw  pulp. 

Esparto  (Stipa  tenacissima  and  Lygeum  Spartum).  The  bast 
fibres  are  grouped  in  bundles  or  filaments  which  are  resolved 
into  ultimate  fibres  by  the  chemical  processes  employed.  HJhe 
fibres  are  shorter  and  more  even  than  those  from  straw/ aver- 
aging about  1.5  mm.  in  length,  and  the  central  canal  is  nearly 
closed.  Serrated  cells  are  numerous  but  considerably  smaller 
than  those  from  straw,  while  the  smooth,  thin-walled  cells  are 
absent.  The  chief  characteristic  which  distinguishes  esparto 
from  straw  and  other  fibres  is  the  presence  of  small  tear-shaped 
cells  derived  from  the  hairs  on  the  surface  of  the  leaves. 

The  composition  of  esparto  is  given  by  Miiller  as  follows: 


Spanish 

African 

Water  . 

Per  cent 
Q.^8 

Per  cent 

8.80 

Cellulose   . 

48.2<; 

34.80 

Fat  and  wax  

2  .07 

2.62 

Aqueous  extract  
Ash  

IO.IQ 

3  -72 

9.81 
3.67 

Pectous  substances 

26    3Q 

2Q    3O 

Cross  and  Bevan  1  give  the  percentage  of  cellulose  in  air  dry 

esparto  as  follows:  Percent 

Spanish 58.  o 

Tripoli 46. 3 

Arzew 52.0 

Oran 45. 6 

1  Cross  and  Bevan :  Text  Book  of  Paper  Making. 


BAGASSE  AND   CORN  STALKS  43 

Bamboo.  ^Bamboo  fibres  closely  resemble  those  from  the 
straws  in  many  of  their  characteristics.  "According  to  Raitt1 
the  average  length  of  the  ultimate  fibres  is  from  2.20  mm.  to 
2.60  mm.  according  to  the  variety,  and  the  diameters  are  from 
0.018  to  0.027  mm.  .While  not  so  long  as  spruce  fibres  they 
are  much  longer  than^hose  from  any  of  the  deciduous  treesT] 
Accompanying  the  true  fibres  are  numerous  serrated  cells  and 
ovoid  pith  cells  of  various  sizes  and  shapes.  Cells  similar  to 
the  tear-shaped  cells  of  esparto  have  also  been  noticed.  Many 
of  these  different  cells  are  very  small  and  a  good  proportion  of 
them  would  be  lost  during  the  preparation  of  the  pulp. 

[The  number  of  species  of  bamboo  runs  into  the  hundreds 
and  not  all  of  them  are  suited  for  paper  making  work  because 
of  the  difficulties  in  reduction  to  pulp  and  bleaching  to  good 
color.  (  , 

Rushes.  In  many  districts  there  are  large  areas  of  swamp- 
land densely  covered  with  rushes  of  various  kinds.  Investi- 
gation has  shown  that  the  fibres  in  these  are  very  similar  to 
esparto  and  that  pith  cells  are  also  present  though  they  are  far 
smaller  than  those  from  straw  and  many  would  be  lost  during 
the  washing  and  bleaching  of  the  fibre. 

Examination  of  rushes  from  South  Carolina  showed  that  they 
contained  35  per  cent  of  cellulose  and  that  of  this  about  30 
per  cent  consisted  of  fine  pith  cells  which  would  wash  easily 
through  a  loo-mesh  sieve. 

Rushes  appear  to  require  a  more  drastic  cooking  treatment 
than  straw  or  esparto  and  the  fibres  bleach  a  little  harder.  They 
are,  however,  potential  sources  of  fibre  which  can  be  availed  of 
when  necessity  arises. 

Bagasse  and  Corn  Stalks.  These  two  materials  are  so  similar 
in  their  fibrous  characteristics  and  in  the  treatment  necessary 
in  cooking  them  that  they  may  be  considered  as  practically 
identical.  Bagasse,  the  crushed  stalks  of  ,the  sugar  cane,  is 
produced  in  large  quantities  in  the  sugar  industry}  and  is  gen- 
erally burned  as  fuel,  though  its  value  for  this  purpose  is  com- 

1  Raitt:  Indian  Forest  Records,  Vol.  Ill,  Part  III. 


44  FIBROUS   RAW  MATERIALS 

paratively  low  because  of  its  wet  condition.  It  is  estimated 
that  seven  States  in  the  "corn  belt"  produce  annually  about 
eighty  million  tons  of  corn  stalks  of  which  the  greater  part  is 
practically  a  waste. 

Both  of  these  materials  can  be  reduced  to  a  pulp  quite  easily 
by  the  soda  process  and  the  pulp  will  bleach  to  a  good  white 
color  with  less  than  10  per  cent  of  bleach.  The  ash  in  the  stalks 
is  considerably  lower  than  that  in  straw  and  contains  much  less 
silica,  so  that  its  effect  on  the  recovery  process  is  very  slight. 

The  pulp  from  both  raw  materials  consists  of  long  thick- 
walled  fibres  mixed  with  shorter  fibres  of  similar  structure  and 
cells  of  various  shapes  and  sizes.  These  include  serrated  cells 
of  comparatively  large  size,  long  thick  cells  with  rounded  ends 
and  many  pith  cells  which  are  so  thin-walled  that  nearly  all 
become  flattened  during  the  reduction  process.  These  pith  cells 
are  much  larger  than  those  from  straw  and  are  therefore  much 
more  difficult  to  remove  by  washing.  They  impart  to  the  paper 
made  from  this  fibre  a  hardness  and  rattle  which  are  undesirable 
in  many  products,  and  as  their  separation  from  the  rest  of  the 
fibre  has  proved  very  difficult  the  presence  of  pith  has  proved 
one  of  the  chief  stumbling  blocks  in  the  way  of  using  either 
bagasse  or  corn  stalks. 

Miscellaneous  Materials.  Among  the  many  substances  pro- 
posed as  sources  of  fibre  the  following  may  be  considered  as 
falling  in  this  class:  papyrus  1  which  grows  in  immense  quanti- 
ties along  the  Nile  and  which  yields  about  33  per  cent  of  easy- 
bleaching  pulp  when  cooked  by  the  soda  process;  asparagus2 
waste  from  canning  factories  and  dry  stalks  at  the  end  of  the 
season;  pea  and  bean  vines  3  which  according  to  Reinke  yield 
better  fibre  than  asparagus;  cotton  stalks,  of  which  immense 
quantities  are  burned  every  year,  but  which  so  far  have  never 
been  utilized  successfully;  zacaton,  a  Mexican  grass,  which 
has  been  carefully  investigated  by  the  Bureau  of  Plant  Indus- 

1  Beam:  Chem.  Section  Bull.  No.  2,  Welcome  Tropical  Research  Lab.  Sudan. 

2  Reinke:  Chem.  Ztg.,  1913,  37,  81. 

3  Reinke:  J.  Soc.  Chem.  Ind.,  1913,  594. 


WOODS  45 

try; 1  tropical  grasses,  numerous  species  of  which  have  been 
tried  on  an  experimental  scale  by  Raitt,2  Richmond 3  and  others. 
Many  of  these  have  been  found  to  produce  excellent  fibre. 

Peat  also  might  possibly  be  considered  in  this  class.  Numer- 
ous attempts  have  been  made  to  produce  useful  fibre  from  peat, 
the  treatments  given  ranging  from  an  entirely  mechanical  pro- 
cess, through  treatment  with  alkalis  and  acids,  to  fermentation 
processes.  All  methods  have  thus  far  failed  to  produce  a  fibre 
which  can  be  used  in  anything  but  the  coarsest  products. 

Woods 

The  woody  tissues  of  plants  are  made  up  of  cells  which  exhibit 
great  diversity  of  form,  size,  and  markings  as  the  accompanying 
drawings  Figs,  i  and  2  show.  Those  in  which  the  paper  maker 
is  particularly  interested  are  the  true  wood  fibres,  or  libriform 
cells,  and  the  tracheids,  but  many  of  the  other  cells  are  of  inci- 
dental interest  as  helping  to  identify  the  wood  from  which  they 
were  derived. 

The  wood  fibres  are  always  spindle  or  fibre-form  and  the  walls 
are  relatively  strongly  thickened.  They  never  have  true  spiral 
stria tions;  in  only  a  few  species  do  they  show  pits,  which  are 
generally  elongated  and  oblique.  Wood  fibres  are  variable  in 
length  in  different  woods,  ranging  from  2.0  mm.  to  0.14  mm., 
but  in  all  cases  they  are  the  longest  elements  present.  As  an 
example  of  wood  fibres  may  be  cited  the  chemical  pulp  made 
from  poplar  wood;  this  contains  in  addition  only  the  ducts  and 
rarely  a  few  of  the  small  cells  from  the  medullary  rays. 

Tracheids  are  elongated  and  tapering  cells,  more  or  less  ligni- 
fied  and  having  peculiar  markings  known  as  bordered  pits  or 
discoid  markings.  Fig.  3  shows  these  as  they  appear  on  the 
surface  of  the  fibre  and  illustrates  how  they  are  formed  by  the 
thin  partition  wall  between  two  tracheids.  These  pits  are  so 
constant  in  number  and  mode  of  distribution  that  they  may  be 

1  Brand  and  Merrill:  Bull.  No.  309,  U.  S.  Dept.  of  Agriculture. 

2  Raitt:  Indian  Forest  Records,  Vol.  V,  Part  III. 

3  Richmond:  Philippine  J.  Sci.,  1906,  I,  433-462. 


46 


FIBROUS  RAW  MATERIALS 


FIG.  i    DRAWINGS  OF  WOOD-ELEMENTS 

1-7.  Avicennia  sp.  i.  Wood-parenchyma  cells;  tangential  section.  2.  Sep- 
tum of  a  duct.  3,  4,  5.  Conjugate  wood-parenchyma  cells.  6,  7.  Portions  of 
spirally  striated  libriform  fibres.  8-n.  Bast  cells  of  Cytisus  laburnum.  8. 
Cross-section  through  young  bast  bundle  acted  on  by  chloroiodide  of  zinc.  9,  10, 
ii.  Cross-sections  through  young  bast  cells  similarly  treated.  12.  Porlieria 
hygrometrica;  radial  section  of  conjugate  substitute  fibres.  13.  Jatropha  mani- 
hot,  radial  section  through  wood.  14-18.  Tectona  grandis;  elements  separated 
by  maceration.  14.  Conjugate  wood-parenchyma  cells.  15.  Ordinary  wood- 
parenchyma  fibre.  16.  Substitute  fibre.  17.  Libriform  fibre.  18.  Septate  libri- 
form fibre. 


WOODS 


47 


19 


40 


FIG.  2.    DRAWINGS  OF  WOOD-ELEMENTS 

19.  TracheidfromTectonagrandis.  20-23.  Porlieria  hygrometrica.  20.  Con- 
jugate substitute  fibres  in  cross  section.  21.  Ordinary  substitute  fibre  after 
maceration.  22,  23.  Conjugate  substitute  fibres  after  maceration.  24-27.  Cy- 
tisus  laburnum;  elements  after  maceration.  24.  Wood-parenchyma  fibre.  25. 
Tracheid.  26.  Substitute  fibre.  27.  Simple  libriform  fibre.  28.  Cross -section 
through  cambium  and  youngest  wood  of  Cytisus  laburnum.  29,  30.  Mahonia 
aquifolium;  ducts.  29.  After  maceration.  30.  Longitudinal  section.  31-36. 
Extremeties  of  ducts  separated  by  maceration  from  Hieracium.  37-39.  Ducts 
from  Onopordon  acanthium.  40.  Spirally  marked  duct  from  Vitis  vinif era.  41. 
Libriform  fibre  from  Jatropha  manihot. 


FIBROUS  RAW  MATERIALS 


a, 


3 

'©( 


FIG.  3.    DISCOID  MARKINGS  ON  WOOD  CELLS 

Pinus  laricio;    a.  Radial  walls;    b.  A  transverse  section. 

Pinus  sylvestris;    c.  Development  of  markings;    d,  e.  Transverse  sections  of 
nearly  perfect  and  perfect  discoid  markings. 

used  as  a  distinguishing  characteristic  for  some  woods.  Tin 
cone-bearing  or  coniferous  trees,  such  as  spruce,  fir,  hemlock, 
etc.,  the  wood  consists  almost  entirely  of  tracheids,  and  when 
sulphite  fibre  or  ground  wood  from  such  trees  is  examined  under 
the  microscope  the  discoid  markings  may  be  very  readily  seen. 
These  tracheids  are  generally  much  longer  than  the  librifonn 


u 

FIBRE  LENGTH  49 

fibres  from  other  woods  and  hence  possess  greater  paper  making 
valueVJ 

Sap  and  Heartwood.  The  sapwood,  or  that  of  compara- 
tively recent  growth,  is  usually  lighter  in  color  and  contains 
more  fermentable  material  than  the  older  and  denser  heart- 
wood.  Each  year  a  layer  of  sapwood  goes  over  into  heartwood 
which  becomes  darker  and  harder  from  infiltration  of  coloring 
matters,  resins,  etc.  The  sapwood  is  generally  preferred  for 
pulp  because  it  is  more  easily  reduced  by  either  the  mechanical 
or  chemical  processes.  In  some  woods,  as  fir  and  buckeye,  the 
difference  in  color  and  hardness  between  hear;twood  and  sap- 
wood  is  not  in  evidence. 

Fibre  Length.  The  length  of  the  fibres  or  tracheids  in  a  given 
tree  is  known  to  vary  with  the  position  from  which  the  sample 
was  taken.  This  has  been  very  carefully  investigated  for  conif- 
erous woods  by  Mell,1  who  finds  that  the  length  of  tracheids 
varies  considerably  not  only  in  different  parts  of  the  same  tree, 
but  also  within  the  same  annual  ring  at  the  same  distance  above 
the  ground.  In  both  trunk  and  branches  the  average  length 
increases  from  the  center  outward  until  the  tree  reaches  its 
maximum  height  growth,  after  which  it  remains  quite  constant. 
The  highest  average  length  of  tracheids  in  the  branches  is  usu- 
ally less  than  in  the  trunk.  Tracheids  also  vary  in  length 
according  to  the  character  of  the  soil  and  the  amount  of  mois- 
ture, those  from  trees  growing  in  rich,  moist  soil  being  longer 
than  those  from  trees  grown  in  dry  soil.  Lee  and  Smith 2  have 
also  made  very  careful  studies  along  similar  lines  of  one  or  two 
trees  of  Douglas  spruce.  Their  observations  are  in  general 
confirmatory  of  those  of  Mell,  though  in  some  respects  their 
conclusions  are  different. 

Because  of  these  variable  factors  it  is  very  difficult  to  determine 
the  average  length  of  tracheids  or  of  the  libriform  cells  of  broad- 
leaved  woods.  The  following  table  by  Mell  gives  the  length  of 
tracheids  of  many  of  the  coniferous  woods  of  the  United  States; 

1  Mell,  Paper  Trade  J.,  June  15,  1911. 

2  Forestry  Quarterly,  Dec.,  1916. 


FIBROUS  RAW  MATERIAL 


the  figures  are  the  averages  of  many  measurements  of  samples 
taken  from  different  parts  of  the  trunks  and  branches. 


Names  of  trees 

Length  of  fibres 

Mm.* 
aver. 

Mm. 
Max. 

Mm. 

Min. 

Amabilis  fir  (Abies  amabilis)  . 

3-H 
3.10 
4-63 
4.14 
3-i6 
4.02 

3-63 
2.47 

2  .IO 

2-59 
4.OI 

3-53 
5-71 
3-48 
2-97 
2.87 

2  .06 
2.85 

5  -°6 
5.89 
i  .96 

2-94 
4-13 
4-47 
4-39 
2-63 
5-53 
3-32 
2-35 

2  .IO 
4-03 

3-86 
4.20 

3-53 
3.10 

2-73 
2.68 
6.99 
4.82 
4-69 

2  .02 

3-87 
4.OI 
3-04 

5-62 
4.21 
6.03 
5-70 
4-13 
4.96 
4-38 
3.02 
2.81 

3.80 

4-71 

4-21 

6.94 
4.13 

3.63 

3-72 

2  .40 
4.38 

6-53 
7-i9 
2.56 
3-96 

5-45 
5-86 

5-45 
3-72 
6.69 
3-96 
3-30 
2.89 
4-79 
4-71 
6.36 
4-54 
3-88 
3-96 
3-30 
9-25 
5-95 
5-78 
2-39 
4-54 
5-04 
3-63 

1.49 
l.98 

2-73 
2.89 
2.07 
2.64 
2.56 
i-93 
i-43 
i-73 
2-97 
2.31 
3.06 
2.89 
2.48 
2.31 
1.24 
1.32 
3-72 
4-38 
1.49 
1.90 
2-73 
2-73 
2-73 
1.82 

2-97 
2.48 
1.40 
i-49 

3-22 

2.48 
2.64 

3-22 
2.56 

i-73 
1.82 

4-05 
3-47 
3-63 
i-39 
3-i4 
2.81 

i-73 

Balsam  fir  (Abies  balsamea)  

White  fir  (Abies  concolor)  

Lowland  fir  (Abies  grandis)  

Alpine  fir  (Abies  lasiocarpa)  

Noble  fir  (Abies  nobilis) 

Port  Orford  cedar  (Chamaecyparis  lawsoniana) 

Yellow  cedar  (Chamaecyparis  nootkatensis)  
White  cedar  (Chamaecyparis  thyoides)  

Western  larch  (Larix  occidentalis)  

Incense  cedar  (Libocedrus  decurrens)  

White  spruce  (Picea  canadensis)  

Engelmann  spruce  (Picea  engelmanni)  

Black  spruce  (Picea  mariana)    . 

Red  spruce  (Picea  rubens)  ...    . 

Sitka  spruce  (Picea  sitchensis)  

Knobcone  pine  (Pinus  attenuata)  
Sand  pine  (Pinus  clausa)  

Jack  pine  (Pinus  divaricata)  

Shortleaf  pine  (Pinus  echinata) 

Pifion  (Pinus  edulis) 

Limber  pine  (Pinus  flexilis) 

Spruce  pine  (Pinus  glabra)  .    .      .         .      .      .       

Sugar  pine  (Pinus  lambertiana)  

Silver  pine  (Pinus  monticola)  

Lodgepole  pine    (Pinus  murrayana)  

Longleaf  pine  (Pinus  palustris) 

Western  yellow  pine  (Pinus  ponderosa) 

f  Western  yellow  pine  (Pinus  ponderosa)  

Parry  pinon  (Pinus  quadrifolia)  

Red  pine  (Pinus  resinosa)  

Pitch  pine  (Pinus  rigida)  

Pond  pine  (Pinus  serotina) 

W^hite  pine  (Pinus  strobus)                                            .    .  . 

Loblolly  pine  (Pinus  taeda)                                           .... 

Scrub  pine  (Pinus  virginiana)                              

Red  fir  (Pseudotsuga  taxifolia)                  

Redwood  (Sequoia  sempervirens)  

Bigtree  (Sequoia  washingtoniana)  

Bald  cypress  (Taxodium  distichuwi) 

Arborvitae  (Thuja  occidentalism                    -                    .  . 

Western  red  cedar  (Thuja  plicatd)                                 .  .  . 

Hemlock  (Tsuga  canadensis)                                  

Western  hemlock  (Tsuga  heterophylla)  

*  A  millimetre  is  equal  to  about  one-twenty-fifth  of  an  inch, 
t  From  a  tree  growing  in  dry  soil. 


MOISTURE  IN  WOOD  51 

Among  broad-leaved  woods  the  following  have  been  exam- 
ined by  the  author.  The  measurements  are  for  the  true  wood 
fibres  and  the  samples  were  prepared  from  wood  of  commercial 
size.  All  measurements  are  in  millimetres. 


Wood 

Length 

Width 

Max. 

Min. 

Avg. 

Max. 

Min. 

Avg. 

Beech  (Fagus  atropunicea)  
Poplar  (Populus  grandidentata)  .... 
Aspen  (Populus  tremuloides}  

1.72 
1.62 
1.68 

0.70 
0.71 
0.78 

•13 
.08 
•  i"? 

0.029 
0.044 
o  .046 

O.OI5 
O.O2O 
O  O2O 

O.O22 
O.O28 

o  032 

Cotton  gum  (Nyssa  aquatica)  
Red  alder  (Alnus  oregond) 

2.67 
I  77 

1.24 
o  84 

•85 

22 

O.IOO 

o  038 

O.O28 
O  OI4 

O.O66 
O  O27 

Sycamore  (Platanus  occidentalis]  .  . 
Red  maple  (Acer  rubrum)  . 

2  .21 
I  IQ 

0.94 

o  67 

•57 

O    Q-Z 

0.033 

o  028 

0.016 
o  014 

O.O24 
O  O2O 

Buckeye  (Aesculus  flava)  
Cucumber  tree  (Magnolia  acuminata) 
Umbrella  (Magnolia  fraseri)  
Tulip  tree  (Liriodendron  tulipifera) 
Sweet  gum  (Liquidamber  styraciflua) 
Black  gum  (Nyssa  sylvatica)  
Elm  (  Ulmus  americana]  
Birch  (Betula  papyri/era) 

0.92 
1.30 

i-47 
i-S9 

2  .02 
2.32 

1.08 

I  D3 

0.46 

o-55 
0.62 
0.64 
0.96 
1.18 
1.03 
o  78 

O.62 

0.86 
.08 
•14 
•55 
.68 

•35 

17 

0.026 

0.036 

0.041 

0-035 

0.036 
0.035 

O.O2I 

o  042 

0.014 

O.O2O 
0.013 
O.O2I 
O.O22 
0.015 
O.OI4 
O  OI4 

O.O2O 
O.O29 
O.O27 
O.O29 
0.031 
O.O26 
6.019 

o  02  ^ 

Moisture  in  Wood.  The  cell  cavities  of  all  wood  contain 
large  amounts  of  air  and  moisture.  According  to  Sachs  the 
volume  percentage  of  freshly  cut  fir  wood  is 

Per  cent 

Cell  walls 24. 81 

Water 58. 63 

Air  cavities 16.  56 

The  moisture  in  wood  varies  with  the  amount  of  seasoning 
it  has  had  and  also  with  the  kind  of  wood,  the  position  in  the 
tree,  and  the  time  of  cutting.  Certain  kinds  of  wood  in  the 
living  tree,  as  for  example,  white  ash,  black  locust  and  the 
white  and  red  cedars  are  comparatively  dry;  black  ash  and  the 
oaks  have  about  twice  as  much,  and  chestnut  and  buckeye 
about  three  times  as  much  moisture  as  white  ash;  cypress  and 
white  fir  also  contain  large  amounts  of  water.  In  the  hard 
woods  the  variation  in  moisture  with  the  different  positions  in 


52  FIBROUS   RAW  MATERIAL 

the  tree  is  comparatively  slight  while  the  conifers  show  wide 
variations,  the  heartwood  generally  being  very  dry  and  the 
sapwood  very  wet. 

Seasoning  greatly  reduces  the  amount  of  moisture  present  in 
wood  but  the  rate  of  drying  is  not  the  same  for  all  varieties, 
some  losing  moisture  in  one- tenth  the  time  required  by  others. 
The  term  "air  dry,"  therefore,  is  one  which  may  denote  almost 
any  condition  of  moisture  from  40  per  cent  down  to  4  per  cent 
of  the  total  weight,  according  to  the  length  of  seasoning  and  the 
conditions  to  which  exposed. 

Weight  per  Cubic  Foot.  The  figure  for  weight  per  cubic  foot 
is  one  which  is  closely  connected  with  the  moisture  content, 
since  the  shrinkage  in  volume  due  to  loss  of  moisture  is  not  at  all 
proportional  to  the  amount  of  such  loss.  For  this  reason  it 
is  best  to  base  the  weight  per  cubic  foot  on  the  absolutely  dry 
material.  Determinations  made  by  the  Forest  Service  1  for  a 
number  of  American  woods  gave  the  following  results: 


Kind  of  wood 

Pounds 
per  cubic 
foot  (bone 
dry) 

Kind  of  wood 

Pounds 
per  cubic 
foot  (bone 
dry) 

Balsam  fir 

21     <O 

Jack  pine 

24  oo 

Red  fir               

22  .  2< 

Loblolly  pine,  fall  cut  

28.86 

White  fir   

21  .AO 

White  pine  

2O.  2Z 

Alpine  fir       

22  .OO 

Engelmann  spruce,  Montana 

24  .40 

Lowland  fir  

21  .53 

Engelmann  spruce,  Colorado 

21.28 

Eastern  hemlock 

24.    60 

Sitka  spruce 

23    6O 

Western  hemlock 

24.    80 

White  spruce   .  .  . 

26    4O 

Tamarack 

32    OO 

White  birch     

34   2O 

Lodgepole  pine,  Montana.  . 
Lodgepole  pine,  California 

25-I5 

23    2O 

Poplar  
Black  gum  

24.16 
30  .  36 

The  following  table  of  weights  per  cubic  foot  is  also  from 
data  supplied  by  the  Forest  Service.  In  this  case  the  weights 
are  for  kiln  dried  material  and  the  bone  dry  weights  would 
probably  be  about  4  per  cent  less.  This  table  shows  the  varia- 
tions which  may  be  expected  in  wood  of  the  same  species  when 
grown  in  different  localities  and  under  different  conditions.  It 

1  The  Log  of  the  Lab.,  Dec.,  1916. 


RESINS 


53 


illustrates  the  impossibility  of  establishing  a  figure  for  any  wood 
which  will  apply  in  all  cases. 


Kind  of  wood 

Locality 

Pounds  per 
cubic  foot 
(kiln  dry) 

Cypress,  bald          

Louisiana   .  .  . 

•25 

Douglas  fir   

California,  Oregon,  Washington 

TO—  3  C 

Longleaf  pine  

Florida,  Mississippi  

38-4.2 

Norway  pine 

Wisconsin 

Spruce,  red  

New  Hampshire  

28 

Spruce   white 

New  Hampshire,  Wisconsin 

2  ^—  2Q 

Red  alder   . 

Washington 

27 

Aspen                        

Wisconsin. 

26 

Basswood   

Wisconsin,  Pennsylvania 

24—26 

Beech         :  

Pennsylvania,  Indiana. 

4.1—4.3 

Paper  birch  

Wisconsin  

37 

Buckeye     

Tennessee  

24 

Chestnut  

Maryland  

2Q 

Black  gum 

Tennessee 

3  C 

Red  maple  

Pennsylvania,  Wisconsin  

74—37 

Silver  maple 

Wisconsin 

32 

Sugar  maple 

Indiana,  Pennsylvania 

41—4.2 

Sycamore              ...        ... 

Indiana,  Tennessee.  .  . 

•2  A  —  9  (? 

Tulip  tree  

Tennessee  

27 

Tupelo  

Louisiana  

35 

Resins.  Many  woods  contain  small  amounts  of  volatile  oils 
generally  approaching  terpene  (Ci0Hi6)  in  chemical  composition. 
Practically  nothing  is  known  regarding  their  formation.  From 
these  by  oxidation  are  formed  balsams  and  resins,  the  former 
being  regarded  as  mixtures  of  resins  with  volatile  oils.  There 
are  also  in  some  cases  resins  which  contain  gum  or  mucilage 
and  are  hence  termed  gum  resins. 

The  amount  of  resin  in  wood  varies  greatly  with  the  different 
kinds  .and  with  the  solvent  used  in  its  determination.  With 
Canadian  woods  Richter1  obtained  the  following  results: 


Ether  extract 

Alcohol  extract 

Fresh  balsam 

Per  cent 
o  4^—0  8<? 

Per  cent 
I  .  1^—3  .6^ 

Fresh  spruce 

o  70—1  .80 

o.  70—1  .94 

Richter:  Wochbl.  Papierfabr.,  44  (1913),  4507. 


54 


FIBROUS  RAW  MATERIAL 


Examination  of  the  resins  obtained  gave  the  following  con- 
stants: 


Ether  resin 

Alcohol  resin 

Acid  number 

Saponification 
number 

Acid  number 

Saponification 
number 

White  spruce  

6l 
66 

80 
no 

54 
35 

83 

1  68 

Black  spruce  

Richter  claims  that  storage  of  the  wood  decreases  the  ether 
extract  and  increases  the  alcohol  extract,  while  Schwalbe  and 
Grimm 1  state  that  seasoning  or  passing  air  over  the  chips  reduces 
both  ether  and  alcohol  soluble  material. 

The  ether  extract  is  usually  lighter  in  color  and  more  liquid 
and  sticky  than  the  alcohol  extract.  Part  of  each  is  soluble  in 
petroleum  ether  and  according  to  Johnsen2  it  is  this  portion 
which  is  responsible  in  large  part  for  the  trouble  with  pitch  in 
sulphite  pulp.  The  portion  soluble  in  petroleum  ether  is  a 
thick  yellow  liquid  and  appears  to  be  of  a  fatty  rather  than  a 
resinous  nature;  the  insoluble  part  is  brown  and  brittle. 

The  resin  in  Bohemian  pine  and  its  distribution  in  the  sulphite 
cellulose  made  from  it  have  been  studied  by  Sieber,3  who  found 
that  cooking  removed  4.2  per  cent;  the  knotter,  screens,  sand 
traps,  etc.,  took  out  51.8  per  cent,  while  bleaching  removed 
15  per  cent. 

Proximate  Analysis  of  Wood.  The  following  table  gives  the 
analysis  of  a  number  of  European  woods.4 

1  Schwalbe  and  Grimm:  Wochbl.  Papierfabr.,  44  (1913),  3247. 

2  Johnsen:  Pulp  and  Paper  Mag.  Can.,  1917,  577. 

3  Papierfabr.,  1915,  June  18. 

4  Miiller:  Die  Pflanzenfaser. 


BARK  AND   KNOTS 


55 


Wood 

Water 

Soluble  in 
water 

Soluble  in 
alcohol  and 
benzine 

Cellulose 

Incrusting 
matter 

Black  poplar 

12    IO 

2   88 

I    37 

62    77 

20  88 

Silver  fir 

13    8? 

I    26 

O  Q7 

^6   QQ 

26   QI 

Birch                         .    . 

12.48 

2    65 

I    14 

rr    r2 

28   21 

Willow     

11.66 

2  65 

I  .  23 

ire    72 

28    74. 

Scotch  pine  
Chestnut  
Linden  

12.87 
12.03 

IO.  IO 

4-05 
S'4* 

3  -56 

I.63 
I  .IO 

3  .93 

53-27 
52.64 
C.3  .OQ 

28.18 
28.82 
2Q    32 

Beech 

12    try 

2   41 

o  41 

AC   47 

3Q    14. 

Still  more  complete  analyses  of  seven  American  woods  are 
given  by  Schorger,1  all  percentages  being  based  on  oven  dry 
samples.  Some  of  his  results  follow: 


Solubility  of  wood 

>, 

in 

^.a 

*&  w 

•£» 

a 

| 

Wood 

ia 

*jj 

oj'o 

0   §" 

0    4 

3 

•*J   4> 

!§! 

1 

offi 
£0 

11 
1* 

|E 

a 

"S 

O 

Longleaf  pine  (Pinus  palustris). 

0-37 

7-15 

6.32 

22.36 

0.76 

5-05 

7.46 

^8.48 

Douglas  fir  (Pseudotsuga  taxi- 
folia} 

o  38 

6  50 

i  02 

16  ii 

i  04. 

6  02 

6l    4.7 

Western   larch  (Larix  occiden- 

talis]  .  . 

O    2^ 

1  2    C.Q 

o  81 

22    14 

O    71 

SO3 

10  80 

57  80 

White  spruce  (Picea  canadensis] 

0.31 

2.14 

1.36 

11-57 

i-59 

5-3° 

iQ-39 

61.85 

Basswood  (Tilia  americana]  .  .  .  . 

0.86 

4.07 

i.q6 

23.76 

5-79 

6.00 

z9-93 

61  .24 

Yellow  birch  (Be  tula  lutea)  .... 
Sugar  maple  (Acer  saccharum).. 

0.52 

0.44 

3-97 
4-36 

0.60 
0.25 

19-85 
17.64 

4-3° 
.4-46 

6.07 
7-25 

24.63 
21.7! 

61.31 
60.78 

The  percentages  of  cellulose  given  in  this  table  by  Schorger 
are  considerably  higher  than  the  figures  of  most  other  analysts 
for  the  same,  or  similar,  woods.  They  are  doubtless  more  accu- 
rate because  of  the  greater  pains  taken  with  the  work  and 
because  of  the  more  complete  knowledge  of  the  precautions 
necessary  to  prevent  hydrolysis  of  the  cellulose  and  its  conse- 
quent loss  during  the  analytical  procedure. 

Bark  and  Knots.  The  bark  serves  as  a  protective  envelope 
for  the  stem  and  gradually  increases  in  thickness,  as  a  layer  is 
added  each  year.  It  contains  long  bast  fibres  which  give  strength 

1  Schorger:  J.  Ind.  and  Eng.  Chem.,  1917,  9,  556. 


56  FIBROUS   RAW   MATERIAL 

to  the  bark,  and  cork  cells  which,  because  of  their  impermea- 
bility, are  admirably  suited  to  form  a  protective  covering  for 
the  tissues  beneath.  Bark  often  contains  coloring  matters  and 
tannins,  sometimes  in  sufficient  amounts  to  make  extraction 
profitable.  It  is  only  slightly  acted  upon  by  the  chemical  pro- 
cesses of  pulp  manufacture  and  for  this  reason  is  of  interest  to 
the  paper  maker  chiefly  because  of  the  necessity  for  its  removal. 
Recent  experiments  have  led  to  its  use  on  a  small  scale  as  a 
substitute  for  better  grades  of  material  in  making  roofing  felts 
and  similar  products  and  it  will  probably  eventually  be  quite 
fully  utilized. 

The  loss  in  barking  varies  greatly  with  the  size  and  shape  of 
the  logs,  with  the  care  used  by  the  men  in  charge  of  the  bark- 
ers, and  with  the  type  of  barker  used.  With  disc  barkers  it 
may  amount  to  10  to  25  per  cent  of  the  rough  wood. 

Knots  are  formed  at  the  points  where  the  branches  make  out 
from  the  stem  or  trunk.  They  are  usually  very  hard  and  dense 
and  are  frequently  highly  charged  with  resins  and  coloring 
matters.  They  are  partially  reduced  by  the  soda  process  but 
are  almost  unaffected  by  the  sulphite  process  which  usually 
fails  even  to  soften  them. 

Decay.  The  importance  of  decay  is  becoming  greater  every 
year  because  of  the  increasing  cost  of  wood.  Not  only  does  the 
wood  stored  in  the  yard  decay  but  ground  wood  stored  in  laps 
also  suffers  damage  which  is  estimated  by  the  Forest  Service 
to  amount  to  between  five  and  fifteen  million  dollars  a  year. 
The  decay  of  wood  stored  in  piles  depends  on  the  size  and  form 
of  the  pile,  upon  temperature  and  humidity  and  upon  the  foun- 
dation upon  which  the  pile  is  built.  Small  piles  of  evenly 
stacked  wood  will  not  decay  because  they  are  well  ventilated 
and  dry  out  readily.  Neither  will  the  wood  in  the  interior  of 
large  piles  because  it  is  too  wet";  but  between  these  two  ex- 
tremes is  a  condition  where  the  moisture  is  just  right  and  the 
fungi  flourish  wonderfully.  The  summer,  with  its  high  tem- 
peratures, is  the  time  when  most  of  the  decay  takes  place  and 
practically  no  loss  is  suffered  in  winter. 


The  following  photomicrographs  show  the  characteristic  forms  and  markings  of  a 
number  of  the  typical  paper-making  fibres.  These  photomicrographs,  as  well  as 
those  in  Chapter  X,  were  prepared  by  the  Paper  Section  of  the  Bureau  of  Standards. 


\ 


PLATE  i 

Cotton  (Gossypium)  Magnification  TOO  diameters.      Photographed  by 
Bureau  of  Standards. 


PLATE  2 

Linen  (Linum  usitatissimum)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  3 

Hemp  (Cannabis  sativa)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  4 

Manila  (Musa  textilis)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  5 

Jute  (Corchorus  capsularis)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  6 

Paper  Mulberry  (Broussonetia  papyri/era)  Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards, 


PLATE  7 

Sisal  (Agave  rigida)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


X  '.     - 

PLATE  8 

Rice  Straw  (Oryza  sativa)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  9 

Esparto  (Stipa  tenacissima)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  10 

Bamboo  (Bambusa  arundinacea)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards, 


PLATE  n 

Corn  (Zea  mays)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  12 

Red  Spruce  (Picea  rubens)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards, 


^ 


PLATE  13 

Spruce  Ground  Wood  (Picea  canadensis)  Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards. 


PLATE  14 

Balsam  Fir  (Abies  balsamea)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  15 

Jack  Pine  (Pinus  divaricata)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  16 

Hemlock  (Tsuga  canadensis)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  17 

Douglas  Spruce  (Pseudotsuga  taxi/olio)  Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards. 


PLATE  18 

Aspen  (Populus  tremuloides)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  19 

Yellow  Birch  (Betula  luted)  Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  20 

Beech  (Fagus  atropunicea)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  21 

Chestnut  (Castanea  dentata)  Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  22 

Tulip-tree  (Liriodendron  tulipifera)  Magnification  100  diameters.     Photographed  by 

Bureau  of  Standards. 


PLATE  23 

Sweet    Gum  (Liquidambar  styracifiua)    Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards. 


PLATE  24 

Hard  or  Sugar  Maple  (Acer  saccharum)  Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards. 


PLATE  25 

Soft  or  Silver  Maple  (Acer  saccharinum)  Magnification  100  diameters. 
Photographed  by  Bureau  of  Standards. 


PLATE  26 

Black  Gum  (Nyssa  syhatka)  Magnification  100  diameters.    Photographed  by 
Bureau  pf  Standards. 


KINDS  OF  WOOD  57 

The  actual  loss  of  the  wood  itself  is  not  the  only  serious 
feature,  for  the  handling  of  such  materials  is  expensive  because 
of  the  labor  required  to  cut  out  the  decayed  portions.  As  it  is 
never  possible  to  make  a  complete  separation  some  poor  wood 
gets  into  the  digester,  cutting  down  its  capacity,  injuring  the 
quality  of  the  pulp,  and  using  up  the  cooking  liquors  uselessly. 
Another  serious  feature  is  the  fire  risk  involved  by  the  tinder- 
like  decayed  portions.  It  takes  but  a  spark  to  ignite  suc8 
material  and  it  is  said  to  be  responsible  for  most  of  the  serious 
pulp  wood  fires. 

The  decay  in  wood  yards  can  be  greatly  lessened  by  making 
small  piles  which  will  dry  rapidly  and  by  piling  the  wood  on  a 
foundation  of  crushed  stone  or  gravel  rather  than  on  sod-land. 
Spraying  the  foundation  with  a  disinfectant  is  also  recommended 
by  Haas.1  Another  point  is  the  careful  removal  of  old  bark, 
decayed  wood  and  the  like;  such  materials  should  never  be 
left  to  be  covered  by  new  wood. 

Kinds  of  Wood.  The  woods  most  generally  employed  in  the 
United  States  for  the  manufacture  of  both  ground  wood  and 
chemical  fibre  are  spruce  and  poplar,  but  the.  growing  scarcity 
of  these  two  species  has  led  to  the  use  of  many  other  kinds. 
The  quantities  of  such  other  woods  depend  on  the  factors  of 
price,  length  of  fibre,  ease  of  reduction  and  the  relative  loca- 
tions of  the  mill  and  the  source  of  the  wood  supply.  The 
questions  of  length  of  fibre  and  weight  per  cubic  foot  have 
already  been  treated  and  we  shall  now  consider  briefly  some  of 
the  woods  which  are  in  actual  use  or  which  have  been  tried  out 
sufficiently  on  an  experimental  scale  to  demonstrate  their  value. 
The  names  and  ranges  of  the  various  species  have  been  taken 
from  Sudworth's  "  Check  List  of  the  Forest  Trees  of  the  United 
States,"  while  the  other  data  have  been  collected  from  widely 
scattered  sources.  The  species  mentioned  comprise  only  a  por- 
tion of  those  which  will  probably  be  found  suitable  for  the 
manufacture  of  paper  or  pulp  in  some  of  its  forms. 

1  Haas:  J.  Soc.  Chem.  Ind.,  1910,  29,  415. 


58  FIBROUS  RAW  MATERIAL 

Spruces.  Red  spruce,  Picea  rubens,  ranging  from  Nova 
Scotia  to  North  Carolina  and  Tennessee,  and  white  spruce,  Picea 
canadensis,  are  the  common  pulp  woods  of  the  East.  The  range 
of  the  latter  is  from  Newfoundland  to  Hudson  Bay,  and  north- 
westward to  Alaska;  southward  to  Northern  New  York,  Michi- 
gan, Wisconsin,  Minnesota,  South  Dakota,  Montana  and  British 
Columbia.  Both  woods  are  light,  soft,  straight  grained  and 
fairly  free  from  resin.  Very  similar  in  quality  are  Engelmann 
spruce,  Picea  engelmanni,  ranging  from  northern  Arizona  through 
the  Rocky  Mountain  region  to  British  Columbia,  and  Sitka  spruce, 
Picea  sitchensis,  extending  on  the  coast  region  from  Alaska  to 
northern  California.  This  latter  species  is  said  to  be  the  best 
pulp  wood  on  the  Pacific  coast. 

All  the  spruces  are  reduced  easily  by  the  sulphite  or  sulphate 
process  but  with  considerably  more  difficulty  by  the  soda  pro- 
cess. The  soda  fibre  is  very  hard  to  bleach.  Because  of  the 
uniformly  light  color  of  the  wood  all  are  admirably  adapted  for 
the  preparation  of  ground  wood,  Sitka  spruce,  however,  being 
somewhat  inferior  to  the  others  in  color. 

Firs.  Balsam  fir,  Abies  balsamea,  occurs  from  Newfoundland 
and  Labrador  westward  to  the  region  of  Great  Bear  Lake  and 
southward  to  Pennsylvania. 

Its  wood  is  very  light,  soft,  not  strong,  rather  coarse  grained, 
and  not  durable.  It  is  frequently  cut  and  used  with  spruce, 
sometimes  to  the  extent  of  20  per  cent  or  more,  in  the  manu- 
facture of  sulphite.  The  fibre  is  considered  somewhat  inferior 
to  that  from  spruce  and  is  likely  to  contain  more  pitch.  Bal- 
sam fir  can  be  successfully  used  in  the  preparation  of  ground  ' 
wood  of  good  color  but  its  use  is  not  favored  because  of  the 
low  yield  per  cord  and  its  tendency  to  decay. 

Other  firs  which  are  found  largely  on  the  Pacific  coast  and  in 
the  Rocky  Mountain  region  are  lowland  fir,  A  bies  grandis;  white 
fir,  Abies  concolor;  amabilis  fir,  Abies  amabilis;  noble  fir,  Abies 
nobilis,  and  red  fir,  Abies  magnified. 

The  wood  of  most  of  these  is  light,  soft  and  straight  grained; 
it  varies  in  the  different  species  from  fine  to  moderately  coarse 


PINES  59 

grained.  All  of  these  trees  grow  to  comparatively  large  size 
and  yield  excellent  pulp  wood.  With  the  proper  treatment  all 
can  be  satisfactorily  reduced  by  the  sulphite  process  with  the 
production  of  long  fibre  similar  to  spruce  in  quality.  White  fir 
is  already  being  so  treated  commercially  and  yields  a  long  silky 
fibre  of  the  highest  quality.  All  of  these  firs  can  be  used  for 
preparing  ground  wood  for  news  print  work  though  the  color 
of  the  product  is  in  most  cases  rather  inferior  to  that  of  spruce 
ground  wood. 

Pines.  Longleaf  pine,  Pinus  palustris,  ranges  from  southern 
Virginia  to  Florida  and  eastern  Texas  and  northward  to  north- 
eastern Alabama  and  northwestern  Georgia.  Covering  a  con- 
siderable portion  of  the  same  territory  is  shortleaf  pine,  Pinus 
echinata.  The  wood  of  both  is  hard,  strong,  dense,  durable  and 
resinous  and  is  much  used  for  many  grades  of  lumber.  It 
cannot  be  cooked  successfully  by  the  sulphite  process  because 
of  its  resinous  nature,  but  if  treated  by  the  soda  or  sulphate 
process  it  yields  a  very  strong,  long-fibred  stock  suitable  for 
wrapping  or  kraft  papers  but  not  for  bleaching. 

Jack  pine,  Pinus  divaricata,  is  found  from  New  Brunswick 
to  New  Hampshire,  westward  through  the  Great  Lake  region 
to  the  Rocky  Mountains  and  south  into  northern  Maine,  New 
York,  Indiana,  Illinois  and  central  Michigan.  It  is  not  suitable 
for  use  in  the  sulphite  process  but  is  largely  used  for  the  pro- 
duction of  kraft  pulp  by  the  sulphate  process.  This  wood  also 
yields  a  fair  grade  of  ground  wood. 

Other  pines  which  are  either  used  commercially  or  which 
have  been  proved  by  semi-commercial  tests  to  be  suitable  for 
use  in  the  sulphate  or  ground  wood  processes  are:  white  pine, 
Pinus  strobus;  western  yellow  pine,  Pinus  ponder osa;  lodgepole 
pine,  Pinus  murrayana;  loblolly  pine,  Pinus  taeda;  scrub  pine, 
Pinus  mrginiana  and  red  or  Norway  pine,  Pinus  resinosa. 
These  pines  may  be  reduced  by  the  soda  process  but  the  treat- 
ment required  is  considerably  more  severe  than  that  given 
poplar  and  the  fibre  is  not  easily  bleached. 


60  FIBROUS   RAW  MATERIAL 

Hemlock  (Tsuga  canadenis).  Range.  —  Nova  Scotia  to  Min- 
nesota, Wisconsin,  Michigan  and  southward  in  the  mountains 
of  the  Atlantic  region  to  northern  Alabama  and  Georgia. 

The  wood  is  light,  soft,  brittle,  not  strong,  crooked  grained, 
liable  to  wind-shake  and  splinter  and  is  not  durable;  its  color  is 
light  brown  tinged  with  red,  the  sapwood  usually  somewhat 
darker. 

This  wood  is  used  to  a  considerable  extent  in  the  sulphite 
process  and  yields  a  fibre  very  similar  to  spruce  though  the 
treatment  has  to  be  rather  more  severe  than  for  spruce.  It  also 
yields  a  good  grade  of  kraft  fibre.  In  the  ground  wood  process 
a  fair  grade  of  fibre  can  be  produced,  though  it  is  considerably 
more  difficult  to  handle  than  spruce. 

A  related  species,  western  hemlock,  Tsuga  heterophylla,  has 
fine-grained,  pale  yellowish  brown,  light,  soft  wood  which  works 
like  white  pine.  It  yields  a  good  grade  of  sulphite  fibre  and  for 
ground  wood  is  far  superior  to  eastern  hemlock. 

Larch  or  Tamarack,  (Larix  laricina).  Range.  —  From  New- 
foundland and  Labrador  to  northern  Pennsylvania,  Indiana, 
Illinois,  central  Minnesota  and  northwestward  to  Hudson  Bay. 

Wood  very  heavy,  hard,  strong,  rather  coarse  grained,  dur- 
able in  contact  with  the  soil;  color  light  brown,  the  sapwood 
nearly  white. 

Larch  is  reduced  by  the  sulphite  process  with  some  difficulty 
and  if  mixed  with  spruce  or  hemlock  is  likely  to  cause  chips 
and  shives.  By  the  sulphate  process  it  can  be  made  into  a 
good  grade  of  kraft  fibre;  it  also  yields  a  good  grade  of  ground 
wood  except  for  color  which  is  a  decided  grayish  green. 

Douglas  Spruce  (Pseudotsuga  taxi/olio) .  Range.  —  From  the 
Rocky  Mountain  region  and  northward  to  central  British 
Columbia. 

The  wood  varies  widely  in  character  and  grain  which  may  be 
very  coarse,  medium  or  fine.  The  coarse-grained  wood  is  usu- 
ally reddish  brown,  while  the  fine-grained  is  clear  yellowish 
brown.  The  wood  is  slightly  resinous  and  resembles  pine  in 
many  of  its  characteristics. 


WHITE   BIRCH  6 1 

Douglas  spruce  has  been  found  well  suited  for  making  kraft 
pulp  and  is  already  used  commercially  in  the  sulphite  process, 
though  it  is  not  so  easy  to  cook  and  bleach  as  spruce. 

Poplar  (Populus  gran didentata) .  Ranges  from  Nova  Scotia 
through  New  Brunswick,  southern  Quebec  and  Ontario  to  north- 
ern Minnesota;  southward  to  Delaware,  southern  Indiana  and 
Illinois. 

The  wood  is  light,  soft,  not  strong,  close  grained,  compact, 
decays  rapidly;  color  light  brown,  the  sapwood  nearly  white. 
This  is  the  wood  most  commonly  used  in  the  soda  process;  it  is 
almost  never  used  in  sulphite  mills  though  it  is  readily  reduced 
by  that  process.  It  yields  a  ground  wood  of  fair  color  but  of 
rather  short  fibre. 

The  three  following  species  are  very  similar  to  poplar  in 
character  of  wood  and  are  of  practically  identical  paper  making 
value. 

Aspen  (Populus  tremuloides) .  Range.  —  Southern  Labrador 
to  Hudson  Bay  and  northwestward  to  the  Mackenzie  River 
and  Alaska;  southward  to  Pennsylvania,  northeastern  Mis- 
souri, southern  Nebraska,  and  throughout  the  western  moun- 
tains to  northern  New  Mexico  and  Arizona  and  central  California. 

Balm  of  Gilead  (Populus  balsamifera) .  Range.  —  Coast  of 
Alaska  and  valley  of  Mackenzie  River  to  Hudson  Bay  and 
Newfoundland;  southward  to  northern  New  England  and  New 
York,  central  Michigan  and  Minnesota,  northwestern  Nebraska, 
northern  Montana,  Idaho,  Oregon  and  Nevada. 

Cottonwood  (Populus  deltoides).  Range.  —  From  Quebec  and 
Vermont  through  western  New  England  and  New  York,  Penn- 
sylvania, Maryland,  and  Atlantic  States  to  western  Florida  and 
west  to  the  Rocky  Mountains. 

White  Birch  — Gray  Birch  (Betula  populifolia).  Range.— 
From  Nova  Scotia,  New  Brunswick,  and  Lower  St.  Lawrence 
River  southward  to  Delaware  and  westward  through  northern 
New  England  and  New  York  to  Lake  Ontario. 

The  wood  is  light,  soft,  not  strong,  close  grained,  not  durable; 
color  light  brown  with  thick,  nearly  white  sapwood. 


62  FIBROUS   RAW  MATERIAL 

This  wood  is  easily  reduced  to  pulp  by  the  soda  process  and 
the  fibre  bleaches  readily.  The  chief  difficulty  in  its  use  is  in 
the  economical  removal  of  the  bark. 

Paper  Birch  (Betula  papyri/era).  Range.  —  From  Labrador 
to  Hudson  Bay,  Great  Bear  Lake,  Yukon  River  and  coast  of 
Alaska;  southward  to  New  York,  northern  Pennsylvania,  cen- 
tral Michigan  and  Minnesota,  northern  Nebraska,  Dakota, 
northern  Montana  and  northwestern  Washington. 

The  wood  is  light,  strong,  hard,  tough  and  close  grained;  its 
color  is  light  brown  tinged  with  red  and  the  sapwood  is  nearly 
white.  The  bark  is  removed  from  this  wood  with  some  diffi- 
culty and  as  even  the  inner  bark  causes  dirt  in  the  pulp  it  must 
be  very  completely  removed. 

Paper  birch  cooks  by  the  soda  process  with  a  little  more 
difficulty  than  poplar  and  the  fibre  requires  slightly  more  bleach. 
It  yields  pulp  similar  to  poplar  and  fully  equal  to  it  in  quality. 

Red  Alder  (Alnus  oregond).  Range.  —  From  Sitka  through 
the  coast  ranges  of  British  Columbia,  Washington  and  Oregon 
to  California. 

The  wood  is  light,  brittle,  fine  grained ;  color  pale  reddish- 
brown. 

By  the  soda  process  this  wood  cooks  readily,  yielding  a  fibre 
very  similar  to  poplar. 

Beech  (Fagus  atropunicea) .  Range.  —  Nova  Scotia  to  Lake 
Huron  and  Northern  Wisconsin;  south  to  western  Florida  and 
west  to  southeastern  Missouri  and  Texas. 

The  wood  is  very  hard,  strong,  tough,  very  close  grained,  not 
durable  in  contact  with  soil,  inclined  to  check  on  drying;  color 
dark  or  light  red  with  nearly  white  sapwood. 

Beech  cooked  by  the  soda  process  requires  about  the  same,  or 
possibly  a  little  more  severe  treatment' than  poplar.  The  pulp 
is  soft  and  easily  bleached,  though  not  quite  so  easily  as 
poplar. 

Chestnut  (Castanea  dentata).  Range.  —  From  southern  Maine 
to  nortwestern  Vermont,  southern  Ontario  and  the  southern 
shores  of  Lake  Ontario  to  southeastern  Michigan;  southward 


SWEET  GUM  63 

to  Delaware  and  southeastern  Indiana  and  on  the  Allegheny 
Mountains  to  central  Kentucky  and  Tennessee,  central  Ala- 
bama and  Mississippi. 

The  wood  is  light,  soft,  not  strong,  coarse  grained,  liable  to 
check  and  warp  in  drying,  easily  split,  very  durable  in  contact 
with  soil.  It  is  reddish  brown  in  color. 

Chestnut  wood  contains  tannin  which  can  be  profitably  ex- 
tracted for  use  in  tanning  or  other  industries.  The  extracted 
chips  can  be  reduced  quite  readily  by  the  soda  process  and  the 
fibre  bleaches  without  much  difficulty.  If  the  tannin  is  not 
removed  the  fibre  is  hard  to  bleach.  Chestnut  fibre  is  short 
and  is  used  as  a  substitute  for  poplar. 

Cucumber  Tree  (Magnolia  acuminatd).  Range.  —  From  west- 
ern New  York  through  southern  Ontario  to  Illinois  and  south 
in  the  Appalachian  Mountains  to  southern  Alabama  and  north- 
eastern Mississippi;  central  Kentucky  and  Tennessee. 

The  wood  is  soft,  light,  not  strong,  close  grained  and  easily 
worked;  color  light  yellow  with  nearly  white  sapwood. 

This  wood  reduces  easily  by  the  soda  process  giving  a  fibre 
closely  resembling  poplar  in  its  paper  making  value. 

Tulip  Tree  (Liriodendron  tulipifera) .  Range.  —  From  Rhode 
Island  to  southwestern  Vermont  and  west  to  Lake  Michigan; 
south  to  Florida,  southern  Alabama  and  Mississippi. 

The  wood  is  light,  soft,  brittle,  not  strong,  easily  worked;  its 
color  is  light  yellow  or  brown  with  creamy  white  sapwood. 

Tuliptree  is  readily  reduced  by  the  soda  process,  yielding  a 
fibre  which  is  similar  in  character  to  poplar  though  generally  a 
trifle  longer. 

Sweet  Gum  (Liquidamber  styraciflua).  Range.  —  From  Con- 
necticut to  southeastern  Missouri  and  Arkansas;  south  to  Florida 
and  Texas. 

The  wood  is  heavy,  hard,  not  strong,  straight  and  close 
grained,  inclined  to  shrink  and  warp  badly  in  seasoning;  color 
bright  brown  tinged  with  red,  sapwood  nearly  white. 

Sweet  gum  can  be  treated  by  the  chemical  processes  about  as 
easily  as  poplar:  the  fibre  is  considerably  longer  than  poplar 


64  FIBROUS   RAW  MATERIAL 

but  not  long  enough  to  bring  it  into  the  class  with  spruce  and 
other  coniferous  woods. 

Sycamore  (Platanus  occidentalis).  Range.  —  From  south- 
eastern New  Hampshire  and  southern  Maine  to  northern  Ver- 
mont and  Lake  Ontario;  west  to  eastern  Nebraska  and  Kansas, 
and  south  to  northern  Florida,  central  Alabama,  Mississippi, 
and  Texas. 

The  wood  is  rather  light,  hard,  coarse  grained,  not  very  strong, 
very  hard  to  split. 

Sycamore  cooks  easily  by  the  soda  process  and  the  fibre  is 
longer  and  more  slender  than  that  from  poplar;  it  is  said,  how- 
ever, to  give  a  rather  "punky"  paper. 

Sugar    Maple,    Hard    Maple    (Acer    saccharum).     Range.— 
From  southern  Newfoundland  to  Lake  of  the  Woods  and  Min- 
nesota;   south  to  northern  Georgia  and  western  Florida;    west 
to  eastern  Nebraska,  Kansas  and  Texas. 

The  wood  is  heavy,  hard,  strong,  tough  and  close  grained;  in 
color  it  is  light  brown  tinged  with  red. 

By  the  soda  process  it  is  reduced  by  about  the  same  treat- 
ment given  poplar;  the  fibre  is  shorter  than  poplar  but  bleaches 
readily. 

Silver  Maple,  White  Maple   (Acer  saccharinum) .     Range.  - 
From  New  Brunswick  to  western  Florida;    west  to  southern 
Ontario,  through  Michigan  to  eastern  Dakota,  Nebraska  and 
Kansas. 

The  wood  is  moderately  light,  hard,  strong,  close  grained, 
easily  worked  but  rather  brittle. 

It  is  reduced  by  the  soda  process  as  readily  as  poplar  and 
makes  a  paper  of  practically  the  same  quality.  The  fibre  is 
a  little  shorter  than  poplar  and  bleaches  readily. 

Red  Maple  (Acer  rubrum).  Range.  — From  New  Brunswick, 
Quebec  and  Ontario  to  Florida;  west  to  Lake  of  the  Woods, 
eastern  Dakota,  Nebraska  and  Texas. 

The  wood  is  very  heavy,  close  grained,  not  strong;  its  color 
is  light  brown  slightly  tinged  with  red,  the  thick  sapwood  is 
lighter  colored. 


BULK  OF  RAW  MATERIALS  65 

Red  maple  is  slightly  more  difficult  to  treat  than  poplar, 
the  fibre  is  rather  shorter  than  poplar  and  bleaches  a  little 
harder. 

Basswood  (Tilia  americana).  Range.  —  From  New  Bruns- 
wick to  Virginia,  Georgia  and  Alabama;  west  to  Lake  Superior, 
Lake  Winnipeg,  eastern  Dakota,  Nebraska,  Kansas  and  Texas. 

The  wood  is  light,  soft,  not  strong,  very  close  grained,  com- 
pact and  easily  worked;  color,  light  brown  tinged  with  red. 

It  is  very  easily  reduced  by  the  soda  process  and  yields  an 
easy  bleaching  pulp  very  similar  to  poplar. 

Black  Gum  ( Nyssa  syhatica) .  Range.  —  From  Maine  to 
Florida  and  west  to  southern  Ontario,  southern  Michigan,  south- 
eastern Missouri  and  Texas. 

The  wood  is  heavy,  soft,  strong,  fine  grained,  very  difficult 
to  split;  in  color  it  is  light  yellow  or  nearly  white. 

By  the  soda  process  it  cooks  nearly  as  easily  as  poplar  and 
yields  a  fibre  free  from  shives.  It  bleaches  a  little  harder  than 
poplar.  Its  fibre  is  longer  than  that  from  poplar  and  makes 
an  excellent  paper.  A  very  white  ground  wood  can  be  made 
from  it  but  it  has  not  sufficient  strength  for  newspaper  work. 

Bulk  of  Raw  Materials. 

This  is  an  important  factor  to  be  considered  in  the  trans- 
portation, storage  and  cooking  of  the  different  materials  yet 
very  few  figures  have  apparently  been  published.  The  follow- 
ing notes  therefore  make  no  claim  to  completeness  but  are 
merely  an  attempt  to  collect  in  one  place  what  little  informa- 
tion is  available. 

Rags.  Bales  of  rags  as  received  at  the  mill  have  been  found 
to  have  the  following  weights: 

Lbs.  per  cu.  ft. 

Egyptian  rags 37.  5 

Blue  cottons 26.  5 

White  cottons 19.  5-22.  i 

When  dusted  and  dumped  into  bins,  but  not  tamped,  they 
weigh  15.6  Ibs.  per  cu.  ft.  before  cutting. 


66 


FIBROUS  RAW  MATERIAL 


Straw.    Weighings  of  rice  straw  gave  the  following  results: 

Lbs.  per  cu.  ft. 

As  baled  for  shipment 1 1 

Chopped  and  tamped 4.7 

Chopped  and  not  tamped 3.3 

Esparto.  Beadle  and  Stevens l  give  the  figures  for  esparto 
as  1 20  cu.  ft.  per  ton  when  pressed  as  usual  or  90  cu.  ft.  from 
hydraulic  presses. 

A  boiler  of  540  cu.  ft.  capacity  (vomiting  type)  will  hold  50 
cwt.  of  esparto,  which  after  cooking  will  occupy  a  volume  of 
300  cu.  ft. 

Wood.  The  number  of  cubic  feet  of  solid  wood  per  cord 
and  the  consequent  weight  per  cord  vary  greatly  with  the 
different  kinds  of  wood  and  the  size  of  the  logs.  Graves 2  gives 
the  following  table  for  the  number  of  solid  cubic  feet  for  sticks 
of  various  diameters. 


Solid  cubic  feet  per  cord  of 

Diameter  of 

No.  of  sticks 

sticks 

per  cord 

Hardwoods 

Softwoods 

Mixed 

Ins. 

6.8 

94 

102.40 

102.40 

IO2  .40 

6.0 

126 

94-72 

98.56 

96.00 

4-75 

205 

88.32 

97-28 

92.16 

3-5 

378 

79.36 

90.88 

84.48 

Measurements  by  the  author  on  carefully  stacked  poplar 
wood  in  four-foot  lengths  also  illustrate  the  same  point: 


Average  diam- 
eter of  sticks 

No.  of  sticks 
per  cord 

Weight  per  cord, 
air  dry 

Per  cent  moisture 

Weight  per  cord, 
bone  dry 

Ins. 
11.72 
7-90 
3    18 

35-5 

70-5 

Lbs. 

4295 
3610 
262=; 

34-2 
29-3 
19.7 

Lbs. 
2828 

2553 
2108 

Sound  poplar  wood  when  chipped,   blown  into  a  bin  and 
leveled  off  but  not  tamped  occupied  a  space  of  259  cu.  ft.  per 

1  Beadle  and  Stevens:  Chem.  News,  1914,  109,  302-304. 

2  Graves:  Forest  Mensuration,  p.  105. 


BULK  OF  RAW  MATERIALS  67 

cord  of  wood  for  an  average  of  three  tests.    The  chips,  when 
placed  loosely  into  a  measuring  box,  weighed  10.8  Ibs.  per  cu.  ft. 
and  if  thoroughly  shaken  down  but  not  tamped  13.8  Ibs.  per 
cu.  ft. 
Spruce  wood  gave,  in  the  case  of  one  test,  the  following  figures: 

One  cord  air  dry  spruce  with  bark  weighs 4500  Ibs. 

Same  after  disc  barking  weighs 3600  Ibs. 

Volume  of  chips  from  above  is 260  cu.  ft. 

One  cubic  foot  of  chips  weighs 13  Ibs. 


CHAPTER  III 
RAGS,  ESPARTO,   STRAW,  BAMBOO 

Treatment  of  Rags.  It  is  generally  conceded  that  about 
70  per  cent  of  the  rags  used  in  this  country  are  imported,  while 
the  remaining  30  per  cent  are  collected  chiefly  in  the  larger 
American  cities  where  the  conditions  of  sorting  are  not  con- 
ducive to  cheapness  or  good  results  because  of  the  high  rentals 
for  buildings  and  the  unskilled  labor  which  must  be  employed. 
In  Europe  each  family  keeps  a  separate  bag  for  linen,  woolen 
and  cotton  rags.  These  are  collected  at  frequent  intervals  and 
are  sorted  and  packed  in  large  sheds  which  are  rented  cheaply, 
thus  securing  less  costly  and  more  satisfactory  grading. 

The  grades  of  rags  differ  in  different  countries  and  vary 
from  time  to  time.  Among  those  listed  in  current  trade  jour- 
nals are  the  following,  which  may  be  taken  as  generally  char- 
acteristic. 

-    Domestic  Foreign 

No.  i  New  white  shirt  cuttings  New  white  cuttings 

No.  2  New  white  shirt  cuttings  Unbleached  cottons 

Fancy  new  shirt  cuttings  Light  flannelettes 

New  blue  cottons  New  mixed  cuttings 

New  mixed  cottons  New  dark  cuttings 

New  black  cottons  White  linens,  Nos.  i,  2,  3,  4 

New  light  second  cottons  Old  extra  light  prints 

No.  i  Whites  Ordinary  light  prints 

No.  2  Whites  Medium  light  prints 

House  standard  whites  Dutch  blue  cottons 

Soiled  standard  whites  'German  blue  cottons 

Thirds  and  blues  German  blue  linens 

Black  stockings  Checks  and  blues 

Dark  cottons 

The  moisture  in  baled  rags  as  received  at  the  mill  has  been 
found  from  a  long  series  of  tests  to  vary  from  7  to  16  per  cent 

68 


TREATMENT  OF  RAGS 


70  RAGS,  ESPARTO,  STRAW,  BAMBOO 

with  an  average  of  about  10  per  cent.  While  rags  are  never 
purchased  on  the  basis  of  a  definite  percentage  of  moisture,  as  is 
wood  pulp,  they  should  be  tested  at  intervals  to  see  that  they  are 
not  intentionally  wetted  with  the  object  of  defrauding  the  buyer. 

The  first  process  in  the  mechanical  treatment  of  rags  is  gener- 
ally a  dusting  or  thrashing.  The  bales  are  opened  and  the 
loosened-up  rags  thrown  into  the  thrasher,  which  is  usually  a 
rapidly  revolving  cylinder  covered  with  teeth  or  spikes  enclosed 
in  an  outer  cylindrical  casing  also  fitted  with  teeth.  There  are 
various  types  of  dusters  but  the  object  of  all  is  to  free  the  rags 
from  loose  dirt  and  deliver  them  sufficiently  clean  for  the  next 
operation,  which  is  that  of  sorting  into  the  numerous  arbitrary 
grades  maintained  at  the  mill  in  question.  This  second  grad- 
ing is  desirable,  because  they  are  frequently  very  imperfectly 
sorted  before  baling  as  is  shown  by  tests  on  seven  different 
lots  of  linens,  which,  when  examined  at  an  American  mill,  were 
found  to  contain  from  10.5  to  45  per  cent,  by  weight,  of  cottons. 
During  this  sorting  the  larger  rags  are  usually  cut  into  two  or 
three  pieces,  the  seams  are  opened  and  buckles,  buttons,  hooks, 
iron,  rubber,  etc.,  are  removed.  Considerable  skill  and  judg- 
ment are  required  to  sort  and  grade  rags  correctly  and  much 
of  the  success  of  subsequent  operations  depends  on  the  care 
with  which  it  is  done.  The  next  step  in  the  process  is  that  of 
cutting  the  sorted  rags  into  pieces  2  to  4  inches  square.  This 
is  generally  done  by  machinery  though  for  the  very  highest 
grades  hand  cutting  is  preferred  because  it  gives  cleaner  stock. 
Machine  cutting  causes  greater  waste  in  the  form  of  dust  and 
many  bits  of  rag  are  also  lost;  the  rags  are  also  more  stringy 
and  do  not  empty  from  the  rotary  as  quickly  as  hand  cut  rags. 
After  cutting,  the  rags  are  given  a  final  dusting  in  some  form  of 
willow  which  permits  the  dust  to  pass  through  the  wire  covering 
while  the  cleaned  rags  are  delivered  into  cars  and  are  ready  to 
be  conveyed  to  the  boilers. 

The  object  of  the  boiling  process  is  to  dissolve  or  saponify 
the  grease,  loosen  up  the  dirt  and  other  impurities  so  that 
they  may  be  easily  washed  out,  and  destroy  or  so  modify  the 


TREATMENT  OF  RAGS  71 

coloring  matters  that  they  may  be  easily  bleached.  Another  im- 
portant duty  is  that  of  destroying  any  wool  which  was  not 
removed  during  sorting.  The  agents  used  to  effect  these  changes 
are  caustic  lime,  caustic  soda  or  a  mixture  of  lime  and  soda  ash. 
The  question  of  which  to  use  is  largely  one  of  personal  pref- 
erence and  of  the  type  of  boiler  used.  Lime  is  only  slightly 
soluble  in  water,  one  part  dissolving  in  1500  parts  of  water  at 
212°  F.  or  in  728  parts  at  68°  F.  It  forms  insoluble  compounds 
with  the  grease  and  other  impurities  in  the  rags  and  is  thus 
removed  from  solution,  but  as  soon  as  it  is  precipitated  a  fresh 
portion  dissolves  to  take  its  place  so  that  the  strength  of  the 
solution  is  practically  constant  throughout  the  boiling.  This 
slight  solubility  of  the  lime  limits  the  speed  of  reaction  and  the 
only  way  to  make  up  for  it  is  to  increase  the  time  of  treatment. 
On  the  other  hand,  it  prevents  injury  to  the  fibres  from  too 
great  concentration  of  alkali  and  is  therefore  more  likely  to 
give  good  results  when  the  usual,  unscientific,  hit-or-miss  methods 
of  control  are  employed. 

Caustic  soda  acts  in  the  same  way  as  lime  except  that  it  is 
readily  soluble  in  water  and  the  compounds  formed  also  remain 
in  solution  and  are  therefore  more  easily  washed  out.  Because 
of  the  complete  solubility  of  caustic  soda  its  use  subjects  the 
rags  at  first  to  strong  solutions  which  continually  diminish  in 
strength  as  the  treatment  continues.  If  the  caustic  soda  used 
is  the  chemical  equivalent  of  the  lime  generally  employed  the 
rags  will  probably  be  overcooked  and  tender  and  the  yield 
low,  but  if  the  caustic  soda  is  used  in  smaller  amounts  and  the 
time  of  boiling  properly  regulated  there  is  no  reason  to  think 
that  it  will  give  inferior  fibre  or  a  lower  yield  than  a  lime  cook 
on  the  same  stock.  Lime-boiled  rags  are  brighter- in  color  than 
those  boiled  with  soda  but  this  difference  frequently  disappears 
after  bleaching.  The  rapidity  with  which  the  alkali  is  used 
up  in  a  soda  boil  is  shown  by  the  following  condensed  data 
from  large  scale  experiments  by  Beadle.1 

1  Chem.  News,  1901,  84,  257. 


RAGS,  ESPARTO,   STRAW,   BAMBOO 


Rags 

Gals, 
per 
cwt. 

Liquor, 
per  cent 
Na2O 

Per  cent 
Na2O  on 
rags 

Free  NazO  at  hours  below,  start 
being  100  per  cent 

i 

2 

3 

4 

5 

i  and  2  cottons  .  .  . 
2nd  cottons  
3rd  cottons  

24 

25-7 
22-22.5 

23-25 

0-33 
0.654 
0.55-0.90 
0.91-1.36 

0.697 
1.68 
1.22-1.78 
1.91-2.45 

38 
48 
31-70 
25-80 

15 

24 

21-43 
16-24 

8 

19 
13-26 

9-i9 

10-23 
7-13 

•-I3 

Linens 

The  severity  of  the  treatment  given  rags  varies  greatly  in 
different  mills  and  with  the  grade  of  rags  and  the  kind  of  paper 
to  be  produced.  The  caustic  soda  necessary  is  given  by  dif- 
ferent authorities  as  from  i  to  10  per  cent,  while  the  use  of  lime 
varies  from  5  to  20  per  cent  on  the  weight  of  the  rags.  The 
steam  pressure  runs  from  15  to  50  Ibs.,  with  30  Ibs.  as  probably 
a  fair  average,  while  the  time  of  boiling  ranges  from  2  to  14 
hours,  and  in  some  cases  has  been  as  much  as  30  hours.  Lime 
necessitates  longer  cooks  than  soda  but  the  tendency  in  all 
cases  is  toward  the  shorter  cooks  since  the  steam  consumption 
is  less  and  the  yields  and  the  capacity  of  the  plant  are  greater. 
Watt 1  gives  the  European  practice  as  1 2  hours  at  30  Ibs.  steam 
pressure  using  216  to  378  Ibs.  of  lime  and  114  to  190  Ibs.  of  48 
per  cent  soda  ash  for  4000  Ibs.  of  rags.  In  general  it  may  be 
said  that  dark-colored  or  very  dirty  rags  require  much  more 
severe  treatment  than  new  cuttings  or  clean,  light-colored  stock. 

The  presence  of  starch  in  new  cuttings  is  said  to  interfere 
with  the  boiling  by  gelatinizing  and  preventing  the  penetration 
of  the  alkali.  It  has  been  proposed  to  get  around  this  diffi- 
culty by  the  use  of  malt  to  hydrolyze  and  remove  the  starch. 
The  rags  are  boiled  with  water  to  swell  the  starch,  cooled  to 
60°  C.  by  adding  cold  water,  and  an  infusion  of  malt  is  then 
added.  In  one  to  two  hours  hydrolysis  is  sufficiently  complete 
so  that  alkali  may  be  added  arid  the  boiling  completed  in  the 
usual  way. 

The  lime  used  should  slake  rapidly  and  completely  and  should 
be  as  free  as  possible  from  iron.  It  is  generally  conceded  that 

1  Watt:  Art  of  Paper  Making. 


TREATMENT  OF  RAGS  73 

its  value  for  this  work  is  in  proportion  to  its  content  of  avail- 
able calcium  oxide.  In  preparing  it  for  use  it  should  be  slaked 
and  run  into  the  boiler  through  wire  sieves  to  take  out  any 
lumps.  Griffin  and  Little  1  give  the  following  analysis  of  lime 
as  representing  an  excellent  grade  for  rag  boiling. 

Per  cent 

Silica,  etc.,  insoluble  in  acid o.  01 

Iron  and  alumina  (Fe2Os  and  AljOs) o.  28 

Lime  (CaO) 92.81 

Magnesia  (MgO) 2.28 

Moisture,  Carbonic  Acid,  etc.  (by  difference) 4.62 

100.  oo 

The  volume  of  milk  of  lime  added  to  a  rotary  boiler  is  gener- 
ally enough  to  fill  it  from  one-half  to  two-thirds  full  after  the 
rags  are  in.  If  the  rags  are  not  covered  by  the  milk  of  lime, 
but  are  exposed  to  the  steam,  they  may  become  tender  and 
brittle. 

Several  types  of  boilers  are  used  for  cooking  rags;  spherical 
or  cylindrical  rotary  boilers  and  stationary  boilers  in  which  the 
circulation  of  the  liquor  is  maintained  either  by  a  pump  as  in 
the  Mather  kier  or  by  a  vomiting  pipe  which  is  connected 
with  a  false  bottom.  In  this  case  the  steam  enters  under  the 
false  bottom  and  in  passing  up  the  pipe  carries  along  the  cooking 
liquor  which  is  then  distributed  over  the  charge  by  baffle  plates. 
The  stationary  type  of  boiler  is  fitted  with  a  safety  valve  and 
there  is  therefore  less  danger  of  explosion  than  with  the  rotaries. 
It  is  claimed  that  there  is  less  loss  of  fibre  because  the  rags  are 
not  in  motion  and  hence  there  is  no  rubbing  off  of  the  weaker 
fibres.  On  the  other  hand,  they  require  more  steam,  are  not 
suitable  for  use  with  lime  cooks  and  take  longer  to  discharge, 
since  the  cooked  rags  must  all  be  removed  by  hand  through 
manholes.  Stationary  boilers  are  largely  used  in  Great  Britain 
but  seldom  on  the  Continent  or  in  this  country. 

Of  the  rotary  boilers  the  cylindrical  is  more  generally  em- 
ployed than  the  spherical,  though  the  shape  of  the  latter  greatly 
assists  in  discharging  its  contents.  The  boilers  are  charged 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  152. 


74  RAGS,  ESPARTO,   STRAW,   BAMBOO 

through  manholes  and  with  large  boilers  the  men  frequently 
enter  them  in  order  to  pack  the  rags  properly.  The  steam 
enters  the  boiler  through  the  trunions  and  passes  through  grat- 
ings on  the  inside  into  the  stock.  The  rotaries  are  also  fitted 
with  strainers  through  which  much  dirt  passes  in  blowing  off 
pressure.  The  rotaries  usually  turn  at  a  speed  of  one  revolu- 


FIG.  5.    SPHERICAL  RAG  BOILER 

tion  in  two  to  five  minutes.  The  consequent  agitation  and 
friction  of  the  rags  cause  the  detachment  of  the  lime  compounds 
formed  and  allow  the  action  to  continue  on  the  remaining  fatty 
materials.  When  the  cook  is  completed  the  liquor  and  steam 
are  blown  off  through  the  strainers  and  blow-off  cocks,  the 
manhole  covers  are  removed  and  the  contents  are  discharged 
by  allowing  the  boiler  to  revolve.  Even  a  large  cylindrical 
boiler  will  empty  itself  clean  in  this  way.  With  competent 
labor  the  operations  on  a  cylindrical  boiler  holding  a  charge  of 
5000  to  5200  Ibs.  of  rags  occupy  the  following  times: 

Hours 

Charging  rags i| 

Blowing  off  liquor .- 2 

Discharging  rags 3 

During  the  cooking  of  rags  a  small  amount  of  ammonia  is 
given  off.  Tests  on  a  large  scale  showed  that  the  following 
amounts  were  discharged. 


TREATMENT  OF  RAGS  75 

o.  22  per  cent  ammonia  (NHs)  from  Japanese  blues, 
o.  05  per  cent  ammonia  (NH3)  from  second  white  stock 
o.  14  per  cent  ammonia  (NH3)  from  clean  white  linen 
o.  33  per  cent  ammonia  (NHs)  from  German  blues 

The  washing  of  the  cooked  rags  is  usually  done  in  large  en- 
gines similar  to  beating  engines.  One  or  more  cylinder  washers 
covered  with  perforated  metal  or  wire  cloth,  frequently  old 
Fourdrinier  wire,  serve  to  remove  the  dirty  water  which  is 
constantly  replaced  by  fresh  water.  If  the  rags  are  allowed  to 
stand  some  time  with  the  lime  on  them  before  washing  they 
become  softer  and  more  absorbent  and  are  better  for  blotting 
papers.  On  the  other  hand,  if  they  are  washed  at  once  they 
are  harder  and  the  color  is  rather  better.  The  lime  compounds 
formed  during  cooking  are  friable  and  easily  washed  out  in 
most  cases  but  occasionally  enough  mineral  oil  is  present  so 
that  they  collect  in  sticky  masses  on  the  sides  of  the  washer, 
fill  up  the  meshes  of  the  wire  on  the  washing  drum,  and  appear 
as  small  globules  in  the  rag  stock  itself.  When  lime  is  used  the 
washing  should  always  be  done  with  cold  water  because  of  the 
greater  solubility  of  lime  at  low  temperatures. 

When  the  water  from  the  cylinder  washer  comes  away  fairly 
clear  the  beater  roll  is  lowered  to  loosen  up  the  remaining  dirt 
and  gradually  reduce  the  rags  to  half  stuff.  If  this  is  done  too 
soon  the  fibre  loss  is  unduly  great  and  the  frayed  out  fibres 
catch  and  hold  the  dirt  and  the  resulting  stock  is  of  poor  color. 
After  the  rags  are  reduced  to  half  stuff  the  bleach  is  added  to 
the  engine  and  the  whole  put  into  drainers  to  complete  the 
bleaching. 

The  amount  of  water  used  in  preparing  rag  stock  is  very  con- 
siderable. Sindall1  states  that  the  water  required  to  wash  the 
rag  stock  for  a  ton  of  paper  is  25,000  to  35,000  gals.  Beadle2 
estimates  the  quantity  used  in  preparing  the  rags  for  one  ton  of 
two  grades  of  paper  to  be  as  follows,  measurements  being  in 
Imperial  gallons. 

1  Sindall:  Paper  Technology. 

2  Beadle:  Chapters  on  Paper  Making,  Vol.  IV. 


76 


RAGS,  ESPARTO,   STRAW,   BAMBOO 


Bank  paper 

Rag  paper 

Boiling  rags  

Rinsing  rags  

I    ZOO 

Washing  in  engines  

40  ooo 

•27  R?o 

Washing  out  bleach.  .  . 

48,000 

43-930 

The  losses  which  rags  undergo  in  making  into  paper  vary 
enormously  with  the  quality  of  the  rags  and  the  treatment  they 
are  given.  The  following  table,  condensed  from  data  in  Hof- 
mann's  "Papier  Fabrikation"  shows  the  losses  in  preparing 
half  stuff  from  different  materials. 


Kind 

Mois- 
ture 

Cutting 
and 
dusting 

Cook- 
ing and 
wash- 
ing 

Beat- 
ing to 
half 
stuff 

Bleach- 
ing 

Total 
loss 

Kilos 
bone  dry 
half  stuff 
per  loo  kg. 
rags 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

White  linens  

e—  7 

4—  e 

7~I  2 

A—  Q 

*~6 

26—3  •? 

67—74 

Bagging  

e—  II 

c—  7 

11-18 

12—  14 

5—  Q 

A2—Z  Z 

eR-Ae 

White  cotton  

4-5 

5 

11-13 

8-9 

4 

34 

66 

Red  and  blue  calico  

6 

6 

12-13 

12-13 

4-5 

40-42 

58-60 

Half  wool  and  old  rags  .  . 

6 

6 

38 

10 

4 

64 

36 

Blue  linen  

6-7 

6 

10-13 

9-14 

4-5 

35-45 

55-65 

Similar  data  from  the  records  of  an  American  book  paper 
mill  using  rotary  boilers  are: 


Kind 

Sorting 
and  tare 

Thrashing 

Cutting 

Total  loss 
to  finished 
paper 

Japanese  blues 

Per  cent 
3    I 

Per  cent 

2    A 

Per  cent 
1  6 

Per  cent 
34   6 

New  calico  

c  a 

A    O 

o  4 

26  .  2 

Belgian  blues  

3   c 

A    Q 

2    8 

42  .  2 

Whites  

I  .  C 

O    2 

z  .0 

25  .5 

Muslins 

7  8 

I    8 

•?   i 

41    7 

Russian  blue  linens 

7    7 

2    ^ 

6  7 

AS    8 

Beadle 1  in  recording  English  practice  gives   the  following 
figures  for  the  losses  on  boiling  and  bleaching. 

1  Beveridge:  Paper  Makers'  Pocket  Book. 


ESPARTO 


77 


Percentage  lost  on 

Boiling 

Bleaching 

Best  new  cottons  

Per  cent 
8.7i 

12.20 
5-80 
12  .50 
23-50 

Per  cent 

3-29' 
7.70 

6.20 

4-30 
13.00 

Low  grade  cottons  

No   i  cotton  rags 

No  3  cotton  rags                                        .  .  . 

New  unbleached  cottons     .             

Esparto.  Esparto,  because  of  its  high  cost,  has  never  come 
into  competition  in  this  country  with  soda  fibre  prepared  from 
woods,  but  in  Europe,  and  more  particularly  in  Great  Britain, 
it  is  one  of  the  most  important  fibrous  raw  materials.  Intro- 
duced^  into  England  in  1860  by  Routledge,  its  use  increased 
from  1 6  tons  in  1861  to  184,000  tons  in  1884,  since  which  time 
about  200,000  tons  have  been  used  every  year,  not  including 
what  is  used  on  the  Continent. 

The  grass  is  imported  in  bales  bound  with  iron  or  twisted 
bands  of  esparto.  These  bales  are  opened  up  and  spread  out 
on  tables  covered  with  iron  netting  to  allow  sand  and  dirt  to 
pass  through,  and  the  grass  is  sorted  by  hand  to  remove  roots, 
weeds,  etc.,  which  are  more  resistant  to  alkali  than  esparto  and 
hence  cause  dirt  and  shives  in  the  pulp.  The  loss  in  dusting 
and  hand  picking  is  i  to  6  per  cent.  The  dust  contains  sand 
and  other  mineral  matter  as  well  as  fat  or  wax  from  the  esparto 
itself.  The  analysis  of  fine  dust  is  given  by  Beveridge 1  as 
follows: 

Per  cent 

Organic  matter  (by  ignition) 64.  6 

Water  (loss  at  212°  F.) 6.  2 

Mineral  matter. 29.  2 

Of  the  organic  matter,  about  90  per  cent  is  of  a  waxy  nature, 
while  the  mineral  matter  or  ash  gave  the  following  analysis: 


1  Beveridge:  Paper  Makers'  Pocket  Book. 


78  RAGS,   ESPARTO,   STRAW,   BAMBOO 

Percent 

Silica  (SiO2) 56. 43 

Calcium  carbonate  (CaCO3) 19. 17 

Magnesium  carbonate  (MgCO3) 3.  76 

Alumina  (A^Os) 20. 57 

99-93 

Machine  cleaning  by  willows  is  also  resorted  to  and  by  some 
is  considered  superior  to  hand  picking.  The  grass  from  the 
willows  goes  directly  to  the  cookers  without  any  further  sorting, 
and  sand  and  uncooked  weeds,  etc.,  are  removed  by  sand  traps 
and  screens  after  cooking. 

The  boilers  used  for  esparto  may  be  merely  open  tubs  since 
little  or  no  pressure  is  necessary  but  the  more  general  practice 
is  to  employ  closed,  stationary  boilers  with  some  device  for  cir- 
culating the  liquor.  Rotary  boilers  are  almost  never  used  as 
they  cause  the  fibres  to  roll  up  into  small  balls  which  beat  out 
with  great  difficulty  and  are  apt  to  cause  lumps  in  the  paper. 
The  capacity  of  esparto  boilers  is  generally  2  to  3  tons  of  grass. 
The  boiler  is  partly  charged  with  lye  and  the  esparto  is  fed  in, 
steam  being  admitted  at  the  same  tune  to  soften  it  and  enable 
a  greater  quantity  to  be  packed  in.  The  grass,  which  is  not 
cut  as  in  the  case  of  straw,  is  charged  through  the  top  and  after 
cooking  is  removed  through  a  side  door  near  the  bottom.  The 
steam  pressure  carried  varies  in  different  mills  from  5  to  50  Ibs., 
and  the  time  of  cooking  from  2  to  6  hours;  the  present  tendency 
seems  to  be  toward  the  higher  steam  pressures. 

As  compared  with  rags  esparto  requires  a  much  greater 
amount  of  alkali,  which  is  invariably  soda,  since  lime  is  never 
used  because  of  the  formation  of  insoluble  compounds.  The 
amount  of  alkali  recommended  by  Dunbar  for  different  grades 
of  grass  is  as  follows : 

Fine  Spanish 16.1-17.9  Ibs.  7°  P61"  cent  caustic  per  100  Ibs.  grass 

Medium  Spanish..  14. 3-16.  i  Ibs.  70  per  cent  caustic  per  100  Ibs.  grass 

Fine  Oran 16.  i  Ibs.  70  per  cent  caustic  per  100  Ibs.  grass 

Medium  Oran.  ...  14. 3-15.  2  Ibs.  70  per  cent  caustic  per  100  Ibs.  grass 

Tripoli 17. 0-17. 9  Ibs.  70  per  cent  caustic  per  100  Ibs.  grass 


ESPARTO 


79 


The  liquor  for  boiling  varies  from  7  to  15  degs.  Tw. 
As  typical  examples  of  actual  cooks  made  under  fairly  good 
working  conditions  Beveridge  1  gives  the  following: 


Spanish 

Tripoli 

Weight  of  charge  

5600  Ibs. 

5600  Ibs 

Caustic  liquor  per  charge,  gals  
Pounds  of  60%  caustic  per  charge  
Steam  pressure,  maximum  

1570 
900 

20  Ibs. 

i57o 

1020 

20  Ibs. 

Time  under  pressure  

2^  hrs. 

3  hrs. 

Yield   unbleached  air  dry  fibre 

44.—  4"?% 

4.1-42% 

When  the  cook  is  completed  the  pressure  is  blown  down  and 
the  liquor  run  off  to  the  recovery  system ;  hot  water  is  then  run 
into  the  boiler  and  the  pressure  brought  up  to  20  to  30  Ibs. 
This  is  again  blown  off,  the  stock  drained  as  dry  as  possible,  re- 
moved, and  conveyed  to  the  washing  system  which  usually 
consists  of  engines  similar  to  those  used  in  treating  rags.  Dur- 
ing washing  much  of  the  cellular  matter  (leaf  hairs)  is  removed 
and  some  short  fibres  are  lost. 

The  bleaching  of  esparto  is  generally  carried  out  in  engines. 
The  bleach  required  varies  from  7  to  12  per  cent  of  the  un- 
bleached fibre  and  often  a  little  sulphuric  acid  is  added  to  the 
engine  about  half  an  hour  after  the  bleach.  When  bleaching 
is  completed  the  stock  is  run  off  on  a  press-pate  which  serves 
the  double  purpose  of  removing  the  bleach  residues  and  de- 
livering the  fibre  in  a  convenient  condition  for  further  operations. 

The  recovery  of  alkali  from  the  waste  liquors  is  conducted 
along  the  same  lines  as  with  the  liquors  from  wood.  Accord- 
ing to  Griffin  and  Little  2  the  silica  in  the  ash  from  esparto 
forms  silicate  of  soda  during  furnacing  and  thus  reduces  the 
per  cent  of  ash  recovered.  A  recovery  of  80  per  cent  is  con- 
sidered good  while  85  per  cent  is  the  most  that  can  be  expected 
under  the  best  conditions. 

1  Beveridge:  Paper  Makers'  Pocket  Book,  p.  76. 

2  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  158. 


8o 


RAGS,  ESPARTO,   STRAW,   BAMBOO 


Straw.  Straw  as  used  in  paper  making  includes  the  stems 
and  leaves  of  the  various  cereals.  '  The  composition  of  straws, 
particularly  with  regard  to  the  amount  of  ash  and  its  constitu- 
ents, varies  greatly  with  the  soil  upon  which  they  were  grown. 
Wolff  1  gives  the  following  analyses  for  different  straws. 


Winter 
rye 


Winter 
wheat 


Sum- 
mer 
barley 


Winter 
barley 


Oats 


Corn 


Per  cent  Per  cent  Per  cent  Per  cent  Per  cent  Per  cent 

Water 14.3  14.2  14.3  14.3  14.3  14.0 

Ash 3.2  5.5  7.0  5.5  5.0  4.0 

Fat  and  wax 1.3  1.5  1.4  1.4  2.0  i.i 

Nitrogenous  matter 1.5  2.0  3.0  2.0  2.5  3.0 

Starch,  sugar,  gums,  etc 25.7  28.7  31.3  28.4  36.2  37.9 

Cellulose 54.0  48.0  43.0  48.4  40.0  40.0 

Beveridge 2  considers  the  cellulose  as  determined  by  Muller's 
method  too  high  and  gives  the  following  percentages  obtained 
by  digesting  the  straw  with  bisulphite  of  soda. 

Per  cent 

French  wheat 41.5 

Zealand  wheat 40. 9 

Dutch  wheat 41.6 

Dutch  oats 42.  o 

Dutch  rye 44.  7 

Dutch  barley 38. 3 

Cross  and  Bevan 3  give  the  percentage  of  bone  dry  cellulose 
on  bone  dry  straw  as  follows: 

Per  cent 

Oats.  . 52.0  and  53.5 

Oats,  foreign 46.  5 

Wheat 49^  6 

Wheat,  foreign 50.  2 

Rye,  foreign 53 .  o 

From  analyses  of  rice  straw  by  Takeuchi 4  the  following  figures 
are  taken: 

1  Wolff:  Landwirtschaftl.     Kalender,  1869,  zitiert  bei  Hugo  Miiller,  Die  Pflan- 
zenfaser,  p.  97. 

2  Beveridge:  J.  Soc.  Chem.  Ind.,  1894,  101. 

3  Cross  and  Bevan:  Text  Book  of  Paper  Making,  1907,  p.  136. 

4  Takeuchi:  Bull.  Coll.  Agric.,  Tokio,  1908,  7,  619-621. 


STRAW 


8l 


Good  harvest 

Poor  harvest 

Hygroscopic  moisture  

Per  cent 

12     •?! 

Per  cent 
98<? 

Dry  matter  

87    69 

QO    I  ^ 

Total  nitrogen 

O   Q7 

I   48 

Crude  protein 

6   O^ 

8  82 

Crude  fat 

I    *6 

i  6c 

Crude  fibre       

ii  16 

i  .05 

28  72 

Crude  ash  
Silica     

11.42 
c    -in 

12.35 
6  i* 

Dextrose  

2  .2< 

i  28 

Sucrose 

O    7Q 

o  06 

Starch  and  hemicelluloses 

14  86 

18  7? 

Pentosans     .... 

14  28 

16  ?< 

Analyses  by  the  author  of  two  samples  of  American  grown 
rice  straw  of  the  " Carolina  Gold"  variety  showed  the  presence 
of  14.5  and  12.4  per  cent  of  ash  of  which  silica  constituted 
81.6  and  79.7  per  cent  respectively. 

The  ash  from  various  straws  shows  the  following  compo- 
sition : 1 


Total 
mineral 

K20 

Na2O 

CaO 

MgO 

Fe2O3 

P205 

SO3 

Si02 

Cl 

Barley,  aver,  of  4 

8.10 

23  -75 

i°92 

7-°53 

2.°62 

2.°I9 

3-94 

3  -91 

51-43 

S-75 

Oat,  aver,  of  8.  ... 

7-77 

38.37 

3-99 

4-23 

2-53 

i-79 

2.66 

3  -06 

35-68 

7-99 

Rye,  aver,  of  3.  ... 
Wheat,  one  test.  .  . 

4-32 
3-25 

26.28 
12.  16 

0.74 
i  .00 

ii  .10 

6.82 

4-45 
4.00 

3-19 
i  .02 

8.97 
3.20 

5-57 
5-78 

36.86 
65-34 

3-68 
0.60 

i  Straw  is  used  for  the  production  of  two  quite  dissimilar  fibrous 
materials;  a  coarse,  yellowish,  half  stuff  which  is  used  for  straw 
boards  and  cheap  wrapping  papers,  and  a  bleached  cellulose, 
similar  to  esparto  in  many  of  its  properties,  which  enters  into 
the  composition  of  numerous  high  grade  products. 

For  the  manufacture  of  straw  boards,  the  straw,  after  dusting 
and  cutting  into  short  lengths,  is  treated  with  milk  of  lime  in 
rotary  boilers.  The  action  of  the  lime  is  not  vigorous,  incrust- 
ing  matters  are  not  separated  from  the  cellulose  to  any  great 
extent  and  mineral  matters  originally  present  in  the  straw  re- 
main practically  untouched  in  the  finished  product.  According 

1  Wolff:  Ashen  analysen. 


82  RAGS,   ESPARTO,   STRAW,   BAMBOO 

to  Kirchner  1  it  is  the  general  practice  in  Germany  to  cook  the 
chopped  straw  in  rotary  spherical  boilers  of  14  cubic  metres 
(494  cu.  ft.)  capacity  which  hold  noo  kilos  (2420  Ibs.)  or  1500 
kilos  (3300  Ibs.)  after  tamping.  The  steam  pressure  varies 
from  45  to  75  Ibs.  and  the  time  of  cooking  from  4  to  5  hours. 
A  yield  of  70  to  80  per  cent  is  obtained. 

In  some  plants  the  lime  is  slaked  and  strained  into  the  boiler 
while  in  others  the  quicklime  is  added  without  slaking.  If  the 
lime  is  poor  a  little  soda  ash  is  sometimes  added.  Rye  and  wheat 
straw  should  not  be  boiled  together  since  wheat  needs  more 
treatment  than  rye.  For  rye  straw  8.5  per  cent  of  quicklime  is 
sufficient  while  for  wheat  10  per  cent  is  required.  It  is  gener- 
ally reckoned  that  there  is  a  loss  of  30  to  35  per  cent  of  fibre 
substance  from  the  dry  straw  to  the  finished  paper. 

According  to  B.  Haas 2  the  chopped  straw  and  liquor  are  fed 
into  the  digester  together  and  gently  steamed  at  the  same  time, 
thus  increasing  the  capacity  of  the  digester  fully  10  per  cent. 
The  digester  should  be  rotated  without  steam  to  distribute  the 
liquor,  then  steamed  with  the  blow-off  cock  open  to  allow  air 
to  escape  and  finally  steamed  at  60  Ibs.  pressure  for  2\  to  3 
hours.  If  handled  in  this  way  it  is  claimed  to  be  possible  to 
cook  wheat  straw  with  6  per  cent  of  lime  while  under  ordinary 
conditions  it  would  require  13  to  15  per  cent.  If  too  much 
lime  is  used  the  resulting  stock  is  "  greasy,"  drains  slowly  and 
clogs  wires  and  felts. 

In  France  considerable  straw  is  said  to  be  treated  by  a  cold 
process  as  follows:  Rye  straw  is  cut  short  and  put  into  large 
rectangular  brjck  wells  where  it  is  just  covered  with  dilute 
milk  of  lime.  Boards  are  put  on,  weighted  down  with  stones 
and  the  whole  left  for  two  to  four  weeks.  It  is  then  taken  out 
and  worked  in  edge  runners  for  at  least  an  hour.  This  product 
is  harder  than  straw  pulp  cooked  by  steaming  at  high  tempera- 
tures and  as  the  knots  are  not  softened  the  grinding  must  be 
done  with  especial  care.  Straw  pulp  prepared  in  this  way 

1  Kirchner:  Das  Papier,  III,  B  and  C. 

2  Der  Papier-Fabr.,  12  (1914),  305-310. 


STRAW  83 

possesses  a  natural  self-sizing  property  which  is  lost  if  the  milk 
of  lime  is  heated  and  is  absent  in  pulp  cooked  by  the  soda  pro- 
cess. Hot  cooked  stuff  requires  much  rosin  size  because  of 
the  presence  of  lime  residues  which  it  is  impracticable  to  com- 
pletely wash  out. 

The  general  American  practice  differs  somewhat  from  the 
German  in  that  the  straw  is  not  cut  and  sorted  before  cooking. 
The  kind  most  generally  used  is  winter  wheat  though  some  use 
rye  and  oat  straw.  It  is  always  received  at  the  mill  in  bales 
which  are  stored  in  large  stacks  near  by;  these  stacks  are  fre- 
quently provided  with  roofs  and  sometimes  with  shelter  on  the 
sides.  There  appears  to  be  little  deterioration  of  the  straw, 
except  on  the  very  outside  of  the  bales  or  in  those  at  the  bottom 
of  the  pile,  and  even  such  straw,  which  has  become  very  dark 
in  color,  is  used  by  adding  a  little  more  lime  to  bring  it  to  the 
right  color.  In  filling  the  rotaries  the  bales  are  broken  up  and 
immediately  fed  in  without  sieving,  cutting  or  any  other  method 
of  preparation;  in  fact  as  much  as  a  quarter  of  a  bale  is  some- 
times added  without  loosening  up  in  any  manner.  This  is 
done  because  it  is  believed  a  larger  charge  can  be  secured.  As 
the  rotary  is  rilled  about  a  gallon  of  water  is  added  for  every 
i\  Ibs.  of  straw.  The  rotary  is  then  revolved  and  steam  ad- 
mitted to  raise  the  charge  to  25  Ibs.  pressure  which  is  main- 
tained for  half  an  hour  or  so.  The  head  is  removed,  more 
straw  added  and  the  charge  again  steamed  or  "wilted"  as 
before.  This  is  repeated  three  or  four  times  so  that  the  final 
charge  is  about  double  that  which  was  first  added.  At  this 
point  milk  of  lime  is  added,  equivalent  to  10  per  cent  calcium 
oxide  (CaO)  on  the  weight  of  the  straw,  after  which  it  is  rotated 
and  brought  up  to  35  to  45  Ibs.  steam  pressure  where  it  is  held 
for  8  to  10  hours.  The  liquor  is  drained  off  under  pressure, 
the  charge  cooled  till  practically  at  atmospheric  pressure,  and 
then  dumped  onto  the  floor  Where  it  is  allowed  to  season  three 
to  five  days  before  being  used.  The  straw  is  washed  about 
four  hours  in  washing  engines,  the  washer  taken  up  and  the 
beating  proceeded  with. 


84  RAGS,  ESPARTO,   STRAW,   BAMBOO 

The  time  required  for  one  cook,  including  charging,  cooking 
and  cooling,  is  about  24  hours.  The  yield  per  ton  of  straw  is 
generally  figured  as  1600  Ibs.  of  board  for  rye,  1400  Ibs.  for 
wheat  and  1200  Ibs.  for  oat  or  rice  straw. 

The  treatment  of  straw  by  the  soda  process  for  the  production 
of  a  high  grade  bleached  cellulose  occupies  an  important  place 
in  the  paper  industry  of  Europe  though  it  is  practically  never 
undertaken  in  this  country.  The  kinds  generally  used  are 
wheat,  oat,  rye  and  barley  straws,  and  of  these  the  first  two 
are  used  most  extensively  in  England.  Since  straw  is  more 
highly  lignified  than  esparto  it  requires  a  more  drastic  treat- 
ment; even  the  knots  must  be  so  reduced  that  they  will  bleach 
readily.  Because  of  this  more  severe  treatment  and  because 
of  the  presence  of  cellular  tissues  which  are  lost  during  the 
washing  process  the  yield  from  straw  is  less  than  that  from 
esparto.  Cross  and  Bevan  1  give  the  practical  yield  as  about 
35  per  cent,  while  Beveridge 2  says  that  a  mixture  of  equal 
quantities  of  barley,  oat,  wheat  and  rye  straws  will  yield  40  to 
41  per  cent  of  air  dry  bleached  cellulose. 

The  straw  cellulose  makes  a  weaker  paper  than  esparto  but 
it  is  suitable  for  mixing  with  rags  or  wood  pulp  for  thin,  hard, 
rattly  papers.  It  tends  to  make  the  stock  "wet"  on  the  wire 
and  imparts  translucency  to  the  papers  in  which  it  is  used. 

In  modern  plants  the  straw  is  cut  by  rotary  cutters  into 
pieces  one  to  two  inches  long  and  freed  from  dust,  grain,  etc., 
by  an  air  blast.  It  is  then  fed  into  the  boilers,  steam  and  alkali 
added  at  the  same  time  assisting  in  packing  the  charge.  Contrary 
to  the  practice  with  esparto  rotary  boilers  are  preferred  for 
straw  because  the  agitation  of  the  charge  permits  a  penetration 
of  the  liquor  which  cannot  be  obtained  in  a  stationary  cooker 
because  of  the  close  packing  of  the  wet  straw.  The  amount  of 
alkali  used  varies  greatly  at  the-  different  mills  and  with  the 
kind  of  straw;  it  may  run  as  low  as  10  per  cent  or  as  high  as 
20  per  cent  of  the  weight  of  the  straw.  Experiments  conducted 

1  Cross  and  Bevan:  Textbook  of  Paper  Making. 

2  Beveridge:  Paper  Makers'" Pocket  Book. 


STRAW  85 

by  the  author  on  rice  straw  proved  that  a  simple  extraction 
with  water  at  20  to  25  Ibs.  steam  pressure  removed  so  much 
material  from  the  straw  that  well  reduced  and  easily  bleached 
fibre  could  be  produced  with  60  to  75  per  cent  of  the  caustic 
soda  necessary  for  unextracted  straw.  Barley  straw  is  said  to 
require  20  per  cent  less  soda  than  oat,  wheat  or  rye  straw.  The 
time  of  cooking  is  variously  given  as  3^  to  8  hours  and  the  steam 
pressure  as  10  to  90  Ibs.;  there  seems  to  be  a  decided  tendency 
toward  the  use  of  the  higher  pressures  of  from  75  to  90  Ibs. 

The  cooked  straw  is  run  or  blown  from  the  boiler  into  wash 
tanks  with  false  bottoms;  these  are  preferred  to  drum  washers 
because  of  the  large  loss  of  fine  fibres  and  cellular  matter  which 
the  latter  cause.  After  washing,  the  straw  is  treated  in  edge- 
runners  to  crush  the  knots  and  it  is  then  bleached  in  much  the 
same  way  as  esparto;  the  bleach  required  is  from  7  to  10  per  cent. 

The  recovery  of  alkali  is  carried  out  in  the  same  way  as  with 
esparto  or  wood  but  the  working  of  the  process  is  rendered 
difficult  in  many  instances  by  the  silica  in  the  straw.  This 
combines  with  the  alkali  forming  sodium  silicate  and  when  the 
recovered  ash  is  causticized  a  bulky,  gelatinous  precipitate  of 
calcium  silicate  results.  This  prevents  settling  in  the  causti- 
cizing  tanks  and  very  greatly  reduces  the  amount  of  soda  which 
can  be  recovered.  A  patented  process  by  Sutherland  and 
Kynaston  proposes  to  precipitate  the  silica  by  adding  bicarbo- 
nate to  the  solution  of  the  recovered  ash;  carbon  dioxide  can 
also  be  used.  They  claim  to  obtain  in  this  way  a  granular 
precipitate  which  can  be  easily  handled,  but  the  process  has  not 
been  an  entire  success. 

Beveridge  1  states  that  the  soda  lost  varies  with  the  amount 
of  silica  in  the  straw,  with  the  composition  of  the  silicate  formed 
and  with  the  amount  of  potash  rendered  soluble.  He  estimates 
that  as  much  as  42  per  cent  of  the  total  soda  in  the  cooking 
liquor  may  be  neutralized  by  the  silica  and  claims  that  when 
the  amount  of  silica  in  the  straw  approaches  3  to  4  per  cent 
of  its  weight  the  recovered  ash  is  of  little  value  for  further 

1  Beveridge:  Paper  Makers'  Pocket  Book. 


86  RAGS,  ESPARTO,  STRAW,  BAMBOO 

digestions.  The  recovery  in  a  Russian  mill  operating  by  the 
sulphate  process  is  claimed  to  be  80  per  cent.1 

Numerous  other  processes  have  been  suggested  for  treating 
straw.  Chlorination  in  stone  chambers,  of  straw  which  has 
been  partially  cooked  with  caustic  soda,  followed  by  a  treat- 
ment with  bleach,  gives  a  high  yield  of  well-bleached,  uniform 
stock,  but  the  process  is  too  costly  and  difficult  to  manage. 
Diess  and  Fournier2  propose  steeping  the  straw  in  acidulated 
water  for  three  hours,  retting  by  organisms  cultivated  from 
African  esparto,  and  finally  cooking  with  strong  caustic  soda 
solutions  —  20°  to  30°  Be.  —  at  45  to  75  Ibs.  steam  pressure 
for  three  to  five  hours.  Reichman 3  treats  the  straw  with  caus- 
tic soda,  washes,  treats  with  hydrofluoric  acid  of  i°  to  2°  Be. 
for  about  five  hours  and  finally  washes  with  dilute  ammonia. 
Probably  the  only  modification  of  the  original  soda  process  which 
has  found  any  extensive  use  is  the  sulphate  process  and  this 
has  been  applied  to  straw  with  notable  success. 

The  sulphite  process  is  not  generally  applied  to  straw,  though 
in  isolated  cases  good  fibre  has  been  prepared  from  it  in  this 
way  and  practical  experience  has  shown  that  it  can  be  employed 
with  excellent  results.  The  general  assumption  that  the  large 
proportion  of  silica  in  the  straw  would  interfere  with  its  treat- 
ment by  the  sulphite  process  is  apparently  not  founded  on  fact. 

Bamboo.  Bamboo,  while  not  of  immediate  interest  in  this 
country,  seems  destined  to  hold  an  increasingly  important  place 
as  a  source  of  fibre  because  of  the  rapidity  of  its  growth  and  the 
high  quality  of  the  paper  which  can  be  made  from  it.  Raitt 4  esti- 
mates that  with  poor  growth  the  annual  yield  of  stems  would 
be  ii  tons,  air  dry,  per  acre  while  with  luxuriant  growth  it  may 
amount  to  as  much  as  44  tons.  He  states  that  in  Lower  Burma 
alone  there  is  an  area  of  about  20,000  square  miles  easily 
available. 

1  Altaian:  Chem.  Ztg.,  1911,  35,  979- 

2  French  Pat.  403,  518. 

3  English  Pat.  12,059,  May  21,  1909. 

4  J.  Soc.  Chem.  Ind.,  1908,  27,  p.  35. 


BAMBOO 


Characteristic  analyses  of  Philippine  bamboos  are  given  by 
Richmond  as  follows: 1 


Structural 
bamboo 

Dwarf  bamboo 

Cellulose 

Per  cent 

P-2       QA 

Per  cent 

Fat  and  wax  

jo  -y4 
o  q6 

DO  •  /J 
I    O3 

Water  extract  

4  Q8 

45q 

Non-cellulose  or  lignin  :  

24  2< 

21     27 

Water 

12    dO 

Ash 

347 

Analyses  of  typical  absolutely  dry  Indian  bamboos  are: 


B.  polymorpha 

B.arundinacea 

C.  pergracile 

Cellulose                     ... 

Per  cent 
CA    71 

Per  cent 
CO    32 

Per  cent 
^2    73 

Fat  and  wax  

I   (X 

I    17 

O  jQ2 

Water  extract  

8  Q5 

8  48 

7   q6 

Pectose  

IQ  .  S5? 

24    3Q 

23    OQ 

Lignin  

J5-74 

15.64 

JS^o 

Ash... 

100.00 
3-97 

100.00 

1.  60 

IOO.OO 

2.57 

By  an  extended  research  on  the  five  most  likely  Indian  bam- 
boos, Raitt3  has  shown  that  by  the  soda  process  yields  of  41.0 
to  43.0  per  cent  of  bleached  fibre  may  be  obtained,  but  the 
bleach  consumption  is  high.  When  the  sulphate  process  is 
used  the  yields  are  42  to  44  per  cent  and  the  bleach  required 
is  much  lower —  15.5  to  18.0  per  cent.  He  finds  the  sulphite 
process  is  unsuited  to  bamboo  because  of  the  difficulty  of  bleach- 
ing the  fibre  and  of  working  with  sulphite  liquor  in  a  tropical 
climate. 

Raitt  overcame  the  difficulties  previously  encountered  with 
bamboo  by  adopting  the  following  treatment: 

(i)  Culms  not  to  be  cut  till  the  shoots  of  the  year  are  full 
grown. 

1  Richmond:  Philippine  J.  SdL,  I,  1906,  1075-1084. 

2  Raitt:  Indian  Forest  Records,  Vol.  Ill,  Part  III,  p.  15. 

3  Raitt:  Indian  Forest  Records,  Vol.  Ill,  Part  III. 


88  RAGS,   ESPARTO,   STRAW,   BAMBOO 

(2)  Seasoning  for  at  least  three  months  before  use. 

(3)  Crushing. 

(4)  Extraction  of  starchy  matter. 

(5)  Digestion  with  sulphate  liquor. 

The  limiting  conditions  of  satisfactory  digestion  for  the  five 
species  investigated  were  found  to  be  20  to  22  per  cent  caustic 
soda  (including  the  sodium  sulphide),  temperatures  of  162  to 
177  degs.,  pressures  of  80  to  120  Ibs.',  and  durations  of  5  to  6 
hours. 

Old  Papers.  In  the  case  of  old  printed  papers  of  the  higher 
grades,  such  as  book  and  magazine  papers,  in  which  there  is  no 
ground  wood,  little  difficulty  is  experienced  in  preparing  them 
for  use  a  second  time.  The  removal  of  the  printer's  ink  can  be 
effected  by  cooking  in  digesters  with  a  caustic  soda  solution 
followed  by  disintegration  and  washing  of  the  pulp.  The  alkali 
removes  the  rosin  sizing  and  saponifies  the  oily  constituents  of 
the  ink  thus  rendering  them  soluble  and  loosening  the  pigments 
so  that  they  may  be  detached  from  the  surface  of  the  fibres 
and  washed  out. 

In  this  process,  as  applied  to  old  magazines  for  instance,  the 
staples  are  removed  by  mechanical  means  and  the  magazines 
fed  into  rotary  digesters.  The  removal  of  the  staples  allows 
them  to  come  to  pieces  sufficiently  so  that  the  alkali  can  pene- 
trate enough  to  reach  all  parts  of  the  paper  and  opening  up 
by  thrashers  is  therefore  not  necessary.  About  3  to  4  per  cent 
of  caustic  soda,  on  the  weight  of  the  papers,  is  then  added 
together  with  enough  water  to  insure  thorough  saturation  of 
the  charge  and  it  is  cooked  at  40  to  50  Ibs.  steam  pressure  for 
a  number  of  hours,  sometimes  as  long  as  13  hours.  After  blow- 
ing down  pressure  the  rotary  is  dumped  and  the  stock  allowed 
to  drain,  after  which  it  is  transferred  to  washers  and  washed 
and  bleached  in  practically  the  same  manner  as  rag  stock. 
The  time  required  for  washing  varies  greatly  with  the  size  and 
condition  of  the  washing  engine,  it  may  even  go  as  high  as  15 
hours  although  this  is  not  usual  if  the  stock  has  been  well 
drained.  The  bleach  required  amounts  to  3  to  4  per  cent  of  the 


OLD  PAPERS  89 

papers  used  and  the  color  obtained  is  usually  a  grayish  white 
because  of  the  impossibility  of  removing  all  traces  of  the  carbon 
from  the  printer's  ink.  This  process  involves  a  considerable 
loss  due  first  to  the  action  of  the  soda  and  steam  in  the  digester 
and  second  to  the  mechanical  loss  of  fine  fibres  and  the  mineral 
fillers  during  the  washing.  The  combined  loss  -from  these 
causes  will  frequently  amount  to  35  to  40  per  cent  of  the 
absolutely  dry  papers  used. 

Similar  results  are  obtained  by  tearing  the  papers  up  some- 
what and  heating  in  large  boilers  with  an  8  to  10  per  cent  solu- 
tion of  soda  ash.  The  temperature  is  maintained  just  below 
the  boiling  point  as  the  object  is  merely  a  surface  loosening  of 
the  ink  and  not  complete  disintegration  of  the  paper  to  a  fibrous 
stock. 

It  has  also  proved  possible  to  eliminate  the  rotary  digester  and 
carry  out  the  entire  process  in  the  beating  engine  or  washer. 
The  printed  papers,  either  plain  or  coated,  are  fed  into  the 
engine  with  water  and  about  2  per  cent  of  caustic  soda  based  on 
the  papers.  When  warmed  to  120°  F.  they  disintegrate  readily 
and  in  a  short  time  the  washing  can  be  started  and  carried  out 
as  usual.  The  color  of  the  stock  obtained  is  better  than  that 
of  the  material  cooked  in  rotaries  and  the  loss  is  probably 
slightly  less.  The  chief  objection  to  the  process  is  that  the  old 
magazines  which  are  largely  used  have  to  be  thoroughly  broken 
up  before  adding  to  the  beater. 

In  either  of  these  processes  ground  wood  has  to  be  carefully 
avoided  because  it  is  turned  brown  by  the  alkali,  yet  is  not 
cooked  enough  so  that  it  will  bleach  to  a  good  color.  Serious 
trouble  has  been  caused  at  times  by  getting  ground  wood  papers 
into  the  rotary  and  it  is  well  to  supply  the  sorters  with  phloro- 
glucin  or  paranitro-aniline  so  that  they  may  test  suspected 
papers  and  throw  aside  all  those  found  to  contain  ground  wood. 
Stock  which  contains  ground  wood,  after  passing  through  the 
rotaries  and  bleachers,  has  the  appearance  of  being  contami- 
nated with  fine,  brown  hairs  or  fibres.  These  are  very  con- 
spicuous when  such  print  papers  are  used  in  a  white  sheet.  It 


QO  RAGS,   ESPARTO,   STRAW,    BAMBOO 

is  interesting  to  note  that  after  cooking  the  ground  wood  is 
just  enough  changed  so  that  it  gives  no  test,  or  at  most  a  very 
faint  pink,  with  phloroglucin. 

This  explains  why  it  has  proved  so  difficult  to  recover  the 
stock  from  old  newspapers,  which  consist  of  approximately 
three-quarters  ground  wood.  The  problem  has,  however,  proved 
very  attractive  to  a  large  number  of  investigators  and  the 
patents  taken  out  are  very  numerous.  Among  the  reagents 
which  it  has  been  proposed  to  use  are  various  alkalis  and  alka- 
line salts,  silicates,  borates,  phosphates,  etc.,  soaps,  peroxides, 
hypochlorites,  alumrnum  chloride,  enzymes  and  inert  materials, 
such  as  clay,  talc,  fuller's  earth,  etc.  These  latter  seem  to  be 
added  to  serve  as  points  about  which  the  pigments  from  the 
ink  may  gather  and  thus  facilitate  their  removal  by  the  washers. 
Most  inventors  are  not  content  with  adding  single  reagents  or 
even  simple  combinations  of  two  or  three,  but  in  cases  use  as 
many  as  eight  different  substances  at  the  same  tune.  Any 
such  combinations  to  be  of  value  in  treating  ground  wood 
papers  must  be  only  weakly  alkaline  and  must  be  used  at  com- 
paratively low  temperatures.  Among  the  materials  which  have 
been  found  best  for  this  purpose  are  fatty  soaps  and  similar 
materials  used  in  con  junction -with  soda  ash  and  sodium  silicate. 

Experiments  have  proved  that  the  disintegration  of  the  printed 
papers  with  the  detergent  in  kneaders  where  comparatively 
dry  conditions  are  maintained  produces  poor  results.  The  pig- 
ment is  set  free  under  such  conditions  that  it  is  ground  into 
the  pores  of  the  fibres  and  it  is  then  almost  impossible  to  wash 
out  enough  of  it  so  that  a  good  color  can  be  obtained.  If  the 
papers  are  disintegrated  and  then  diluted  in  the  washer  before 
mixing  with  the  detergent  much  better  stock  will  result  because 
the  separated  ink  is  then  in  such  a  state  that  it  tends  to  rise 
to  the  surface  and  can  be  more  readily  removed  by  the  washers. 
It  is  evident,  then,  that  a  method  of  disintegration  which  tends 
to  pull  the  ink  from  the  surface  of  the  paper  is  superior  to  one 
which  tends  to  grind  it  into  the  fibres. 

Such  a  procedure  has  been  embodied  in  the  Winestock  process 


OLD  PAPERS  91 

for  the  recovery  of  old  papers.  The  apparatus  used  is  shown  in 
sectional  view  in  Fig.  6  of  a  machine  driven  by  a  direct  connected 
steam  turbine,  M.  The  essential  features  are  a  propeller  tube 
B  at  the  bottom  of  a  cylindrical  tank  A  which  is  mounted 
within  a  chamber  H\  through  the  horizontal  part  of  the  pro- 


FIG.  6.    WINESTOCK  DEFIBERING  MACHINE 
Courtesy  of  Castle,  Gottheil  &  Overton 

peller  tube  extends  a  shaft  which  turns  at  2000  revolutions  per 
minute  and  upon  which  are  mounted  two  propellers  of  different 
pitch.  Between  the  propellers  is  a  baffle  plate  K  to  stop  any 
inclination  toward  a  rotary  motion  of  the  stock  in  the  tube. 

The  papers  to  be  treated  are  opened  up  and  dusted  in  a  rail- 
road duster  or  its  equivalent  and  then  soaked  in  a  tank  of  water 
at  about  160°  F.  either  with  or  without  the  addition  of  soda 
ash  or  other  detergent.  They  are  then  charged  into  the  cham- 


92  RAGS,  ESPARTO,  STRAW,  BAMBOO 

ber  E,  together  with  any  other  additional  detergents  desired, 
such  as  a  mixture  of  soda  ash,  caustic  soda  or  a  soap  composed 
of  tallow,  soda  ash,  caustic  potash  and  silicate  of  soda.  The 
chamber  H  being  full  the  stock  overflows  into  the  cylinder  A 
and  is  circulated  by  the  propellers  back  to  the  chamber  H 
which  it  enters  tangentially  and  through  which  it  circulates  to 
again  enter  A.  The  basic  idea  is  that  the  paper  suspended  in 
water  or  a  weak  alkaline  solution  is  struck  by  the  blades  at 
such  a  speed  that  it  is  unable  to  take  up  the  rapid  motion  and 
is  therefore  pulled  out  or  defibred  while  at  the  same  time  the 
ink  is  loosened  from  the  fibres  by  the  violent  agitation.  The 
second  propeller  has  a  greater  pitch  than  the  first  so  that  there 
is  cavitation  between  the  two  or  a  pressure  on  one  side  of  each 
propeller  and  a  suction  on  the  other.  The  speed  at  which  the 
stock  circulates  is  estimated  at  1200  ft.  per  minute.  Since 
there  is  no  cutting  or  grinding  action  in  this  machine  there  is 
no  shortening  of  the  fibres. 

The  time  of  treatment  necessary  in  this  machine  varies  with 
the  papers  used  and  the  products  desired.  Newspapers  which 
are  to  be  used  for  boards  and  from  which  the  ink  is  not  removed 
require  only  about  fifteen  minutes;  if  the  product  is  to  be  used 
for  white  paper,  and  the  ink  must  be  washed  out,  about  thirty 
minutes  are  required.  Book  and  magazine  papers  need  thirty- 
five  to  forty-five  minutes'  treatment  and  hard  sized  writings  a 
somewhat  longer  time.  The  machine  holds  700  to  900  Ibs.  of 
dry  papers  per  charge  and  requires  from  40  to  60  horse  power. 

Assuming  that  the  papers  have  been  sorted  with  reasonable 
care  and  strings,  bags  and  foreign  materials  eliminated,  the 
Winestock  process  is  suitable  for  all  classes  of  papers,  since  the 
low  temperatures  and  mild  chemicals  do  not  cause  any  serious 
discoloration  of  ground  wood.  As  the  apparatus  liberates  the 
ink  and  color  from  the  fibres  but  does  not  remove  the  loosened 
pigment  a  subsequent  washing  is  necessary. 


CHAPTER  IV 
THE  SODA  PROCESS 

The  principles  upon  which  this  process  depends  are  the  sol- 
vent power  of  the  caustic  soda  for  certain  constituents  of  the 
wood  and  the  hydrolysis  of  other  constituents  resulting,  to  a 
considerable  extent,  in  the  formation  of  products  of  an  acid 
nature  -which  are  then  brought  into  solution  as  salts  of  soda. 
Both  of  these  processes  neutralize  the  alkali  and  by  diminishing 
its  concentration  and  hydrolyzing  power  render  it  useless  for 
further  work  until  it  is  regenerated.  The  reactions  and  de- 
compositions involved  are  of  a  very  complicated  nature  and 
the  products  are  numerous  and  for  the  most  part  ill-defined 
and  little  understood.  The  degradation  of  the  woody  constit- 
uents is  in  general  far  greater  than  for  the  same  constituents 
when  dissolved  by  the  sulphite  process. 

Even  at  low  temperatures  alkali  dissolves  a  very  appreciable 
proportion  of  the  non-cellulose  constituents  while  if  the  tem- 
perature is  raised  the  action  is  greatly  intensified.  Experiments 
on  small  poplar  chips  showed  that  a  3.3  per  cent  solution  of 
caustic  soda  would  dissolve  20.3  per  cent  of  their  weight  by 
twenty-four  hours'  treatment  at  25°  C.  while  if  the  temperature 
were  raiged  to  80°  C.  the  wood  lost  31.6  per  cent  of  its  weight 
in  the  same  time.  Higher  temperatures,  such  as  are  obtained 
by  steaming  under  pressure,  still  further  enhance  the  solvent 
power  of  the  alkali  and  the  speed  with  which  it  acts. 

In  working  with  materials  other  than  wood  due  consideration 
must  be  given  to  pectous  substances.  Working  with  bamboo 
Raitt 1  finds  that  pectose  (matter  soluble  in  i  per  cent  NaOH 
solution  at  100  degs.)  is  easily  soluble  in  boiling  NaOH  solutions 

1  Indian  Forest  Records,  Vol.  Ill,  part  3,  "Bamboo  as  Material  for  Paper-pulp." 

93 


94  THE  SODA  PROCESS 

but  that  it  gelatinizes  at  the  temperatures  employed  in  digestion 
and  is  therefore  likely  to  become  mechanically  attached  to  the 
cellulose  and  is  then  very  difficult  to  wash  out.  Pectose,  fat 
and  wax  grouped  together  neutralize  0.32  per  cent  of  NaOH  on 
the  raw  material  for  each  i  per  cent  found  on  analysis.  Lignin, 
unlike  pectose,  is  not  soluble  in  .weak  solutions  nor  at  tempera- 
tures below  130  degs. 

The  wood  most  used  in  the  soda  process  is  poplar,  at  least  in 
the  northern  part  of  the  United  States,  but  because  of  its  in- 
creasing cost  and  scarcity  other  woods  are  frequently  substi- 
tuted. Among  these  may  be  mentioned  basswood,  maple,  birch, 
cottonwood,  tulip  tree,  sycamore,  several  kinds  of  gum,  chest- 
nut, beech,  etc.  The  best  results  are  obtained  if  the  different 
kinds  are  treated  separately  but  this  is  frequently  impossible 
without  an  excessive  amount  of  labor.  If  mixed  woods  are 
used  it  is  desirable  to  employ  those  which  require  about  the 
same  degree  of  treatment  and  to  keep  the  mixture  as  nearly 
constant  as  possible.  The  mixing  of  woods  which  require 
widely  different  cooking  conditions  invariably  means  diminished 
yield  because  of  the  overtreatment  of  at  least  one  kind  in  order 
that  the  most  difficult  to  reduce  may  be  sufficiently  cooked. 

For  long  fibred  stock,  spruce,  hemlock,  pine  and  white  fir  are 
sometimes  treated  by  the  soda  process.  They  require  more 
alkali  and  longer  cooking  and  yield  less  pulp  than  the  broad- 
leaved  woods.  The  soda  pulp  industry  is,  however,  using  pine 
in  rapidly  increasing  quantities  and  in  this  way  it  is  possible 
to  use  a  number  of  woods  which  are  too  resinous  to  be  treated 
by  the  sulphite  process.  According  to  the  United  States  De- 
partment of  Agriculture  out  of  a  total  of  843,048  cords  of  wood 
used  in  the  soda  process  during  1917,  379,466  cords  were  poplar, 
11,069  cords  were  hemlock,  and  116,267  cords  were  pines  of 
various  kinds. 

On  account  of  the  vigorous  action  of  the  alkaline  solutions 
less  care  is  necessary  in  preparing  the  wood  than  for  the  sulphite 
process.  Knots  are  either  dissolved  by  the  treatment  or  left 
in  such  condition  that  they  are  easily  separated  by  the  screens. 


THE   SODA  PROCESS  95 

Contrary  to  the  usual  belief  the  inner  bark,  however,  is  a  source 
of  trouble  and  should  be  removed  as  completely  as  possible. 
It  cooks  with  difficulty,  uses  up  fully  as  much  caustic  soda  as 
sound  wood,  and  bleaches  with  far  more  difficulty  than  the 
fibre  from  the  wood.  If  the  two  are  cooked  and  bleached 
together  the  resulting  product  is  liable  to  be  contaminated 
with  brown,  stringy  shives.  The  outer  bark  also  uses  up  a 
large  amount  of  caustic  and  in  cooking  breaks  down  into  masses 
of  cells  which  will  not  bleach  to  better  than  a  yellowish  brown 
color  and  hence  cause  dirt  specks  in  the  bleached  pulp.  These 
are  not  the  only  faults  of  bark,  for  its  rough  surface  tends  to 
catch  dirt  from  outside  sources,  such  as  cinders,  sand,  etc.,  and 
transfer  it  to  the  pulp. 

It  is  not  necessary  to  remove  decayed  portions  of  the  wood 
since  they  are  completely  resolved  during  the  cooking  and  do 
no  harm  unless  they  are  of  a  very  black  nature.  Such  decayed 
wood,  however,  gives  a  very  low  yield  of  fibre  and  if  present  in 
large  amount  greatly  reduces  the  output  of  the  digesters,  so 
that  for  this  reason,  at  least,  its  use  is  to  be  avoided.  The  cellu- 
lose in  partly  decayed  poplar  wood  was  found  by  us  to  be  24.9 
and  27.0  per  cent  in  two  samples  as  compared  with  63  per  cent 
for  sound  wood. 

The  wood  is  chipped  by  running  the  logs  diagonally  against 
the  face  of  a  rapidly  revolving  disc  from  which  project  from 
two  to  four  knives.  The  distance  to  which  these  extend  de- 
termines the  length  of  the  chip,  which  for  poplar  is  from  three- 
quarters  of  an  inch  to  an  inch  and  a  quarter.  The  chips  go 
next  to  some  form  of  screen  which  separates  them  into  three 
grades,  dirt  and  very  fine  material,  good  chips,  and  slivers  and 
coarse  pieces.  The^dirt  and  fine  stuff  is  waste,  so  far  as  pulp 
making  is  concerned,  though  it  is  often  used  as  fuel  in  the  boiler 
house,  while  the  slivers  and  coarse  pieces  are  either  crushed  or 
rechipped  and  returned  to  the  screens.  Uniformity  of  cooking 
is  greatly  aided  by  a  uniform  size  of  chips  but  it  is  not  so  essen- 
tial as  in  the  sulphite  process  because  of  the  greater  penetrating 
power  of  the  alkaline  liquor. 


—  Liquor 
Recirculating 
Pipe 


irculafing 
Pump 


FIG.  7.    VERTICAL  DIGESTER,  SECTION  SHOWING  INLETS,  PUMP,  AND  PIPING 
(96) 


DIGESTERS 


97 


The  digesters  used  in  this  process  are  of  the  usual  rotary  or 
stationary  types  but  vary  greatly  in  size  and  capacity.  The 
tendency  is  toward  the  vertical  stationary  type  Fig.  7,  and  away 
from  the  rotaries  since  the  former  effect  savings  in  floor  space, 
power  required  and  time  of  filling  and  emptying.  The  latter  is  a 
very  appreciable  item,  as  a  rotary  holding  3  to  .3^  cords  requires 
three  hours  for  blowing  down  pressure,  discharging  the  contents 
and  refilling  with  chips  and  liquor,  while  a  vertical  digester 


A.  Digester 

B.  Heater  for  cook- 

ing liquor 

C.  Strainer 

D.  Boiler  to  supply 

steam  to  B 

E.  Pump  to  return 

condensed 
water  to  boiler 


G         E 

FIG.  8.    MORTERUD  DIGESTER 

holding  14  to  15  cords  of  wood  requires  only  one  hour  for  the 
equivalent  operations.  The  size  of  rotary  digesters  in  American 
practice  is  generally  about  20  X  7  ft.,  while  the  vertical  digesters 
range  from  27  to  49  ft.  tall  by  7  to  10  ft.  in  diameter;  one  30  X  8 
ft.  will  hold  about  5.5  cords  while  one  49  X  10  ft.  will  hold 
nearly  15  cords  of  wood. 

A  modified  type  of  digester  is  that  used  in  the  Morterud 
system  of  cooking  with  forced  circulation  and  indirect  heating. 
Such  an  outfit  is  shown  in  Fig.  8.  The  steam  in  this  system 
is  not  blown  directly  into  the  charge  but  the  liquor  is  circulated 
through  an  outside  exchange  heater  in  which  steam  is  the  source 


98  THE  SODA  PROCESS 

of  heat.  The  condensed  steam  is  returned  to  the  boiler  as  feed 
water  under  high  pressure  and  at  a  high  temperature.  The 
claims  for  this  process  are  savings  in  coal  and  alkali  and  an 
increased  yield  because  of  the  more  even  temperature  of  the 
cooking  liquor. 

Another  modification  is  that  of  the  jacketed  digester  in  which 
the  steam  for  heating  is  between  the  two  walls.  Experience  has 
proved  that  these  are  very  hard  to  keep  tight  as  the  stays  be- 
tween the  walls  cause  very  frequent  leaks.  No  insulating  cov- 
ering can  therefore  be  used  and  the  steam  consumption  is  very 
high  because  of  the  great  loss  by  radiation. 

The  material  of  the  digesters  is  either  iron  or  steel  and  they 
are  made  either  riveted  or  welded.  The  latter  is  much  to  be 
preferred,  since  the  alkaline  solutions  work  their  way  through 
crevices  which  would  be  impervious  to  water  and  for  this  reason 
a  riveted  seam  is  very  difficult  to  make  perfectly  tight.  As  the 
alkaline  solutions  are  practically  without  action  on  the  material 
of  the  digester  no  lining  is  necessary. 

In  filling  the  digester  the  chips  and  liquor  are  run  in  at  the 
same  time  and  in  order  to  get  in  as  large  a  charge  as  possible 
a  tamping  device  is  sometimes  employed.  This  is  especially 
necessary  for  horizontal  rotaries.  The  time  required  for  charg- 
ing a  rotary  holding  3  to  3^  cords  is  about  one  hour,  while  chips 
from  14  to  15  cords  of  wood  can  be  run  into  a  vertical  digester 
in  15  to  20  minutes. 

The  cooking  liquor  for  the  soda  process  is  merely  a  solution 
of  caustic  soda  containing  a  small' amount  of  sodium  carbonate. 
It  is  generally  made  at  the  mill  by  causticizing  soda  ash  with 
quick  lime.     The  reaction  on  which  the  process  depends  is 
Na2C03  +  CaO  +  H2O  =  2  NaOH  +  CaCO3. 

This  is  a  reversible  reaction  and  the  extent  to  which  the  soda 
ash  is  causticized  depends  on  the  dilution  of  the  liquor.  Ex- 
periments by  Lunge  l  illustrate  the  effect  of  concentration  as 
follows: 

1  Lunge:   Sulphuric  Acid  and  Alkali,  2nd  ed.,  Vol.  II,  p.  750. 


CAUSTICIZING 


99 


Liquor  before  causticizing 

After  causticizing 

Per  cent  Na2CO3 

Speciiic  gravity 

Per  cent  causticity 

2 

5 

10 

14 

20 

1.022  at  15°  C. 
i.  052  at  15°  C. 
1.107  at  15°  C. 
1.  150  at  15°  C. 
1.215  at  30°  C. 

99-4 
99-0 
97-2 
94-5 
90-7 

It  is  obvious  that  the  lower  the  concentration  the  higher  the 
causticity  and  that  therefore  a  demand  for  a  definite  concen- 
tration sets  a  limit  to  the  causticity  attainable.  Attempts  to 
increase  the  causticity  by  boiling  either  under  diminished  or 
increased  pressure  have  met  with  no  success;  practically  all 
causticizing  is  therefore  done  in  tanks  under  atmospheric 
pressure. 

The  type  of  equipment  used  for  causticizing  varies  greatly 
in  the  different  mills;  it  may  be  stated  to  consist  generally  of 
a  wrought  iron  tank  fitted  with  an  agitator  and  frequently  a 
perforated  basket  near  the  top  for  holding  the  lime.  The  tank 
is  filled  with  soda  ash  solution  until  the  bottom  of  the  basket  is 
just  covered;  it  is  then  brought  to  a  boil  and  the  lime  added  to 
the  basket  very  gradually.  As  the  lime  slakes  it  passes  through 
the  perforations  while  stones  or  unburned  cores  are  retained 
and  may  be  easily  removed.  If  the  tank  is  not -fitted  with  a 
basket  the  lime  is  thrown  directly  into  the  hot  soda  ash  solution 
and  slaked  in  the  bottom  of  the  tank.  It  has  been  found  best 
to  boil  with  a  steam  coil  rather  than  by  blowing  steam  directly 
into  the  liquor.  Agitation  with  compressed  air  is  also  not  to 
be  recommended  as  it  reduces  the  causticity  slightly.  The  time 
of  boiling  has  a  considerable  influence  on  the  causticity  obtained 
as  the  latter  increases  with  the  duration  of  the  boil.  The  size 
of  the  plant  in  relation  to  the  necessary  output  frequently 
limits  the  time  of  boiling  but  if  possible  it  should  be  continued 
for  at  least  an  hour;  beyond  this  point  it  is  doubtful  if  the 
gain  in  causticity  will  pay  for  the  extra  expense. 


100  THE  SODA  PROCESS 

Greater  causticity  can  also  be  obtained  in  many  cases  by  in- 
creasing the  agitation.  This  has  been  done  in  certain  instances, 
where  adding  more  wings  to  the  agitator  shaft,  or  increasing  its 
speed,  has  enabled  less  lime  to  be  used  in  obtaining  the  same 
amount  of  caustic  soda.  Tests  on  a  small  scale  have  proved 
that  thorough  agitation  is  to  a  large  extent  equivalent  to  boil- 
ing, and  that  if  the  agitation  is  complete  enough  the  charge 
need  not  be  boiled  at  all  as  a  temperature  of  85  degs.  is  ample. 

The  causticizing  operation  is  generally  carried  out  in  about 
the  following  manner.  The  soda  ash  and  lime  are  boiled  and 
then  allowed  to  settle  in  the  same  tank.  The  clear  liquor  is 
drawn  off  by  an  adjustable  syphon,  more  soda  ash  and  water 
are  added  and  the  sludge  again  boiled  up  and  then  pumped 
over  into  a  second  tank.  The  sludge  from  this  is  flooded  with 
weak  liquor  and  again  boiled  up  and  settled.  Fourth  and  fifth 
boilings  are  made  with  clear  water.  The  clear  liquors  from  the 
first  four  boilings  combined  make  the  cooking  liquor,  while  the 
fifth  boiling  produces  the  weak  liquor  for  a  subsequent  third 
boil. 

The  Dorr  Company  have  recently  proposed  to  causticize 
and  wash  the  lime  mud  in  a  continuous  operation  by  machinery 
similar  to  that  used  in  metallurgical  work.  The  lime  is  crushed 
and  continuously  mixed  in  definite  proportions  with  a  soda 
ash  solution;  the  mixture  then  passes  through  three  reaction 
agitators  which  are  furnished  with  steam  coils  and  then  goes 
to  the  first  thickener.  The  clear  liquor  overflowing  from  this 
goes  to  the  storage  tank  for  cooking  liquor,  while  the  sludge  is 
pumped  to  the  second  thickener  where  it  is  mixed  with  the 
overflow  from  a  third  thickener.  The  clear  liquor  from  the 
second  thickener  flows  to  the  reaction  agitators,  while  the  sludge 
goes  to  the  third  thickener  and  thence  to  waste  or  to  a  recovery 
plant  for  lime.  A  causticizing  plant  of  this  type  is  shown  in 
plan  in  Fig.  9.  A  plant  operated  in  this  manner  has  been  in 
operation  for  some  time  and  is  said  to  be  giving  good  satisfac- 
tion. It  seems  doubtful  if  it  is  very  much  superior  to  a  carefully 
supervised  plant  of  the  ordinary  type. 


doi) 


IO2 


'THE   SODA  PROCESS 


The  lime  mud  produced  in  causticizing  is  generally  a  waste 
^product,  though  there  is  sometimes  a  small  local  demand  for 
agricultural  purposes.  Attempts  have  been  made  to  reburn 
the  mud  and  use  the  lime  over  again  and  a  number  of  plants 
are  now  operating  with  rotary  kilns  similar  to  those  used  in  the 
cement  industry.  The  lime  mud  is  freed  from  water  as  much 
as  possible  by  mechanical  means  and  then  enters  the  kiln, 
through  which  it  passes  in  a  direction  opposite  to  the  combus- 
tion gases.  It  is  first  dried  and  then  heated  to  such  a  tempera- 
ture that  the  carbon  dioxide  is  driven  off  and  the  material 
delivered  as  burned  lime.  A  kiln  7  ft.  in  diameter  and  120  ft. 
long  will  burn  35  to  40  tons  of  lime  per  day,  while  for  capacities 
between  20  and  30  tons  a  kiln  6  ft.  by  100  ft.  is  sufficient.  If 
the  mud  enters  at  55  per  cent  dry,  the  fuel  requirements  will 
be  about  9500  cu.  ft.  of  natural  gas  or  675  Ibs.  of  coal  per  ton 
of  lime  burned. 

In  order  to  keep  the  impurities  down  to  a  reasonable  figure 
it  has  been  found  necessary  to  remove  about  10  per  cent  from 
the  circuit  regularly.  Where  producer  gas  is  used  one  passage 
through  the  kiln  adds  three  pounds  of  impurities  for  every 
100  Ibs.  of  quick  lime,  but  this  only  reduces  the  causticizing 
power  of  the  lime  2  per  cent  because  the  impurities  are  held 
mechanically  rather  than  chemically.  When  powdered  coal  is 
used  instead  of  gas  6  per  cent  of  impurity  is  added  and  this 
reduces  the  causticizing  power  of  the  reclaimed  lime  by  fully 
1 8  per  cent.  The  lime  mud  and  the  reclaimed  lime  from  a  gas- 
fired  kiln  contain  the  following  impurities  for  every  100  Ibs.  of 
available  calcium  oxide;  as  may  be  seen  nearly  all  of  the  im- 
purities added  in  reclaiming  come  from  the  fire  brick  lining. 


Lime  mud 

Reclaimed 
lime 

IVtagnesia  IVtgO 

Per  cent 

Per  cent 

Oxides  of  iron  and  alumina,  Fe2O3  and  A12O3.  .  .  . 
Sodium  oxide,  Na2O                                            .    ... 

1  -3 
0.9 

T      fi 

2.6 

Sulphur  trioxide,  SOs                                        

Silica,  SiO2                                    

2     2 

4^7 

7-7 

COOKING 


103 


The  following  analyses  show  the  composition  of  the  new  lime 
and  the  recovered  lime  from  a  plant  using  natural  gas  as  a  fuel. 


New  lime 

Recovered 
lime 

Calcium  carbonate,  CaCOs  

Per  cent 
4.48 

Per  cent 
3   Ql 

Iron  and  alumina   Fe2Os  and  AUOa 

O    1C 

I   62 

Silica   SiO2 

£ 

O    ID 

O    7O 

Calcium  oxide,  CaO 

92  oo 

8q  c8 

Magnesia   MgO 

2    62 

i  q6 

Undetermined 

O    ZQ 

2    23 

The  recovered  lime  is  in  the  form  of  rounded  nodules  ranging 
up  to  the  size  of  a  hen's  egg.  It  is  often  slightly  greenish  or 
yellowish  in  color  and  slakes  rather  more  slowly  than  good 
lime. 

The  strength  of  the  caustic  liquor  used  in  cooking  varies 
from  8°  to  15°  Be.  at  60°  F.  according  to  operating  conditions. 
Stationary  digesters  require  more  dilute  solutions  than  rotaries, 
while  wet  wood  necessitates  increasing  the  strength  of  solution 
to  counterbalance  the  water  contained  in  the  chips.  If  digesters 
are  heated  by  jackets  or  closed  coils,  weaker  liquors  may  be 
used  because  they  are  not  diluted  by  any  condensed  steam. 
With  direct  heat  in  rotaries  about  700  to  900  gals,  of  liquor 
are  used  per  cord  of  wood  while  in  digesters  the  liquor  amounts 
to  about  800  to  1 100  gals,  per  cord. 

The  boiling  operation  is  a  very  simple  one,  the  object  being 
to  reach  full  pressure  as  soon  as  possible  and  maintain  it  to 
the  end  of  the  cook.  During  this  period  the  air  which  collects 
in  the  top  of  the  digester  is  blown  off  several  times  through 
the  "relief  pipe"  so  that  no  false  pressure  may  be  recorded  on 
the  gauges.  This  "  relief  "  is  usually  not  necessary  when  cooking 
in  rotary  digesters.  The  uniformity  of  the  cook  depends  on 
good  circulation  of  the  liquor  and  in  practice  this  is  obtained 
in  several  ways.  Some  digesters  are  fitted  with  internal  circu- 
lating pipes  on  the  same  principle  as  the  vomiting  pipes  in  rag 
boilers,  while  another  very  successful  and  positive  method  of 


104 


THE  SODA  PROCESS 


circulating  is  to  take  the  liquor  from  below  the  false  bottom 
and  pump  it  up  into  the  top  of  the  digester;  as  both  sides  of  the 
pump  are  under  the  same  pressure  very  little  power  is  required. 
The  steam  consumed  in  cooking  depends  on  the  form  of  the 
digester,  on  whether  it  is  covered  with  an  insulating  covering 
or  not,  and  on  the  size  of  the  charge.  Steaming  may  be  con- 
sidered as  taking  place  in  two  stages,  the  period  in  which  the 
charge  is  being  brought  up  to  pressure,  during  which  the  de- 
mand for  steam  is  very  great,  and  the  period  at  full  pressure 
when  only  enough  steam  is  required  to  make  up  for  the  heat 
lost  by  radiation.  Records  obtained  with  steam  flow  meters  on 
three  sizes  of  digester  gave  the  following  results  in  pounds  of 
steam  required. 


3  -cord  rotary 

6^-cord 
rotary 

iS-cord  vertical 
digester 

While  coming  up  to  pressure  (Ibs.  per  hr.) 
During  period  at  pressure  (Ibs.  per  hr.)  . 
Total  required  during  cook  (Ibs.)  

7,500-7,800 
500 
12,125 

IO,8oo 
1,050 
19,360 

20,OOO-22,IOO 
1,250* 
37,750—44,250 

*  Calculated  by  radiation  formula  for  steam  pipes. 

In  spite  of  the  apparent  simplicity  of  the  process  there  are  a 
number  of  factors  which  greatly  influence  the  results,  and  uni- 
form and  satisfactory  cooking  depends  on  the  proper  adjust- 
ment of  these  variables.  Much  study  has  been  given  to  these 
factors  by  the  author  and  at  about  the  same  time  by  the  Forest 
Products  Laboratory  who  published  a  bulletin l  on  their  re- 
sults. The  following  discussion  "of  the  individual  variables  is 
based  on  the  author's  experiments  which  were  very  carefully 
made  in  special  apparatus  which  enabled  very  close  control  of 
all  conditions  to  be  maintained.  The  experiments  were  all 
made  with  poplar  chips  and  all  yields  are  figured  as  bone  dry 
fibre  on  bone  dry  wood.  Fig.  10  illustrates  the  effect  of  changes 
in  steam  pressure  upon  the  yield  and  the  bleaching  properties 
of  the  fibre  when  all  other  cooking  conditions  are  kept  constant. 

1  U.  S.  Dept.  of  Agriculture,  Bulletin  No.  80. 


STEAM   PRESSURE 


105 


In  this  and  the  succeeding  charts  the  fibres  were  all  bleached 
to  a  standard  color  so  that  the  figures  are  directly  comparable. 
It  is  at  once  evident  that  the  yield  is  greatly  influenced  by  the 
steam  pressure  employed  and  that  the  decrease  in  yield  is  at  a 
nearly  constant  rate  for  pressures  between  70  and  130  Ibs. 
Throughout  this  range  increasing  the  steam  pressure  10  Ibs. 


Per  cent  Bleach 
6789 


130 
a  1  -in 

\ 

\ 

\ 

s 

\ 

\ 

\ 

3 
L| 

j 

! 

LI 
3 

8  90 

\ 

\ 

^ 

\ 

\ 

1 

\ 

\ 

Q 

70 

\ 

N 

\ 

\ 

\ 

\ 

^ 

\ 

34      36      38      40      42      44      46 

Per  cent  Yield 
FIG.  10. 

decreases  the  yield  by  about  i  per  cent  on  the  absolutely  dry 
wood  used.  The  bleach  required  is  practically  constant,  prov- 
ing that  even  70  Ibs.  steam  pressure  will  produce  satisfactory 
pulp.  This  is  contrary  to  the  claims  of  Christiansen 1  who 
states  that  the  minimum  temperature  for  the  production  of 
soda  pulp  is  170°  to  175°  C.  (100  to  115  Ibs.  steam  pressure). 
Probably  this  discrepancy  is  to  be  accounted  for  by  the  differ- 
ence in  the  woods  used. 

1  Christiansen:  Natronzellstoff,  Berlin,  1913. 


io6 


THE  SODA  PROCESS 


A  study  of  the  effect  of  steam  pressure  in  semi-commercial 
cooks  (400  Ibs.  chips)  in  a  vertical,  stationary  digester  gave 
results  following  very  closely  the  form  of  curve  of  the  small- 
scale  cooks.  The  yields  were,  however,  8  to  9  per  cent 


§ 

£  80 

1 

1   * 

1 
1 
1 

g    CO 

III 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

V 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

For  coat  Viold 
FlG.  ii. 

greater,  which  appears  to  be  a  characteristic  difference  between 
the  vertical  digester  and  the  small  rotary  heated  by  a  gas 
flame. 

The  influence  of  the  initial  concentration  of  caustic  soda  in 
the  cooking  liquor  is  shown  in  Fig.  n.  Decreasing  the  con- 
centration increases  the  yield  slightly  but  this  factor  is  evidently 
of  less  importance  than  the  steam  pressure  since  increasing 


SODA    ADDKI) 


107 


from  80  to  100  grams  per  liter  reduces  the  yield  only  about 
1.4  per  cent. 

Fig.  1 2  shows  the  variation  in  yield  and  bleach  required  with 
changes  in  the  per  cent  of  caustic  soda  added.  With  22  per  cent 
of  caustic  the  yield  was  high  but  the  fibre  was  unsatisfactory 


Yiell 

S/ 


11 


32  30 

For  cent  Yield 

15  19 

Per  cont  Bleach 

FIG.  12. 


10 


14 


'IK 


23 


27 


31 


in  that  it  was  commercially  unbleachable.  Increasing  the  caus- 
tic to  28  per  cent  decreased  the  yield  very  greatly  but  produced 
easy  bleaching  fibre.  When  the  caustic  is  brought  up  to  40  to 
50  per  cent  of  the  weight  of  wood  the  form  of  curve  suggests 
that  its  maximum  cooking  effect  is  nearly  reached.  This  curve 
shows  why  25  per  cent  of  caustic  soda  is  the  most  satisfactory 
for  commercial  work  since  if  more  is  used  the  yield  is  too  greatly 
reduced  while  if  much  less  is  employed  the  bleach  required 


io8 


THE   SODA  PROCESS 


increases  to  an  excessive  amount.  Evidently  the  percentage  of 
caustic  soda  is  one  of  the  most  important  points  to  watch  in 
the  control  of  the  soda  process. 

The  influence  of  time  under  pressure  is  shown  in  Fig.  13, 
where  cooks  ranging  from  three  to  nine  hours  are  recorded.  The 
rate  of  decrease  in  yield  is  not  the  same  for  equal  intervals  of 

Per  cent  Bleacfi 
5678 


\ 


\ 


33  35  37  39  41  43 

Per  ceat  Yield 

FIG.  13". 

time  for  an  increase  from  three  to  five  hours  causes  a  greater 
diminution  in  yield  than  an  increase  from  seven  to  nine  hours. 
Considering  the  questions  of  yield  and  bleach  required  the 
time  factor  is  of  much  less  importance  than  either  the  steam 
pressure  or  the  amount  of  caustic  added. 

To  bring  these  charts  onto  a  common  basis  the  table  below 
has  been  calculated  to  show  what  changes  in  the  variable  cook- 
ing factors  will  cause  a  decrease  of  i  per  cent  in  the  yield  ob- 


CAUSTICITY 


109 


tained,  considering  in  each  case  the  entire  range  covered  in  the 
study  of  the  particular  variable.  For  comparison  the  results 
of  experiments  of  the  U.  S.  Forest  Service  l  are  also  given. 


Decrease  in  yield  of  i  per  cent  caused  by 

According  to  experiments  by 

The  author 

U.  S.  Forest  Service 

Increase  of  NaOH  used  by  
Increase  of  time  by  

i  .3  per  cent 
i  .  2  hours 
5.0  Ibs. 
10.  o  gms.  per  liter 

2  per  cent 
i  hour 
5  Ibs. 
13  gms.  per  liter 

Increase  of  steam  pressure  by  
Increase  of  concentration  by  

The  condition  of  the  wood,  whether  very  wet  or  very  dry,  is 
of  importance  in  adjusting  the  strength  of  the  cooking  liquor  as 
already  mentioned.  The  chief  point  to  be  watched  is  the  final 
concentration  of  the  caustic  soda,  taking  into  account  the  moist- 
ure in  the  wood  as  well  as  that  in  the  liquor  itself.  Experi- 
ments have  shown  that  if  this  ultimate  concentration  is  kept 
constant  the  same  yield  will  be  obtained  whether  the  chips 
contain  3  per  cent  or  22  per  cent  of  moisture. 

The  causticity  of  the  cooking  liquor  is  another  factor  which 
is  supposed  to  have  a  large  influence  on  the  cooking  process. 
This  is  probably  true  in  mills  where  the  strength  of  the  cooking 
liquor  is  regulated  by  the  hydrometer  test  or  by  the  titration 
for  total  alkali.  If  the  volume  to  be  added  is  based  on  either 
of  these  tests  the  actual  caustic  soda  added  may  not  be  enough 
to  cook  the  wood  thoroughly  and  the  low  causticity  will  at 
once  be  blamed.  As  a  matter  of  fact  it  makes  no  difference  in 
the  yield  or  bleaching  properties  of  the  fibre  whether  the  caus- 
ticity is  80  or  99  per  cent  provided  liquor  enough  is  present  to 
supply  the  correct  amount  of  actual  caustic  soda.  This  is  also 
true  of  salt,  which  is  sometimes  present  because  of  the  use  of 
electrolytic  caustic,  or  may  even  be  added  intentionally  with 
the  idea  of  protecting  the  fibre  and  increasing  the  yield. 

It  is  of  course  true  that  the  causticity  of  the  cooking  liquor 

1  U.  S.  Dept.  of  Agriculture,  Bulletin  No.  80. 


110  THE   SODA  PROCESS 

has  a  considerable  effect  upon  the  economy  of  the  cooking  and 
recovery  processes  since  the  carbonate  is  carried  through  the 
system  as  so  much  inert  material  which  must  be  handled  by 
the  evaporators  and  black  ash  burners  and  is  subjected  to  a 
loss  of  10  to  20  per  cent  during  each  cycle.  It  has  been  esti- 
mated that  in  a  plant  making  70  tons  of  fibre  per  day,  each 
increase  of  i  per  cent  in  causticity  means  an  annual  saving  of 
about  $500. 

In  diluting  the  liquor  to  the  proper  strength  for  use  it  is  the 
custom  of  some  mills  to  add  a  certain  proportion  of  black  liquor. 
This  is  done  with  the  idea  of  more  completely  utilizing  the 
alkali  in  the  black  liquor  and  of  obtaining  a  more  concentrated 
liquor  to  go  to  the  recovery  system.  As  it  is  in  direct  line 
with  the  production  of  brown  "kraft"  fibre  it  is  logical  to  ex- 
pect that  the  bleaching  properties  of  the  fibre  would  suffer, 
and  this  has  been  found  to  be  actually  the  case  where  black 
liquor  has  been  added  to  the  charge  for  cooking  poplar.  If 
8  per  cent  of  the  total  liquor  consists  of  black  liquor  the  bleach 
required  is  found  to  increase  from  8.4  to  10.1  per  cent,  while  if 
17  per  cent  of  black  liquor  is  added  the  fibre  requires  1-4.1 
per  cent  of  bleach.  If  no  fresh  liquor  is  used,  but  the  entire 
charge  is  made  up  of  black  liquor  brought  to  the  correct  strength 
by  adding  solid  caustic  soda,  the  fibre  produced  requires  at  least 
22  per  cent  of  bleach.  While  the  bleaching  properties  of  the 
fibre  suffer,  the  yield  of  unbleached  fibre  is  increased  by  about 
3  to  4  per  cent  by  the  use  of  8  to  17  per  cent  of  black  liquor. 

The  study  of  the  time  factor  in-  cooking  immediately  brings 
up  the  question  of  how  rapidly  the  reaction  between  the  wood 
and  the  caustic  soda  takes  place.  Fortunately  this  reaction 
can  be  followed  very  readily  by  means  of  analyses  of  the  black 
liquor.  If  the  causticity  of  the  liquor  as  added  is  known  the 
consumption  of  caustic  soda  may  be  calculated  at  any  time 
from  the  black  liquor  analysis  by  means  of  the  following  formula: 

Y      r      BxC 

A   =  C ? 


RATE  OF  REACTION 


III 


where      X  =  per  cent  NaOH  used  up,  based  on  the  bone  dry 

wood, 

A  =  per  cent  causticity  at  the  start, 
B  =  per  cent  causticity  at  time  of  sampling  black  liquor, 
C  =  per  cent  NaOH  added  on  bone  dry  wood. 

Fig.  14  shows  graphically  the  results  of  three  such  studies 
on  poplar  wood.  Curve  A  was  obtained  from  a  vertical  sta- 
tionary digester  holding  400  Ibs.  of  wood,  B  is  from  a  rotary 
digester  holding  about  3  cords,  while  C  is  from  a  vertical  sta- 


3  4 

Time  in  Hours 


FIG.  14. 

tionary  digester  of  a  capacity  of  14.5  cords  of  wood.  All  three 
cooks  were  made  at  no  Ibs.  steam  pressure  and  the  ratio  of 
wood  to  alkali  was  the  same  for  all.  In  each  case  the  percent- 
age of  caustic  soda  consumed  is  based  on  the  bone  dry  wood 
used.  The  weight  of  wood  used  in  the  largest  digester  was 
estimated  from  the  average  weight  of  a  cord  of  poplar,  but  in 
the  other  two  cooks  the  chips  were  accurately  weighed;  this 
may  have  introduced  a  slight  error  into  curve  C  but  this  would 
merely  alter  its  position  on  the  chart  and  would  not  change 
its  form. 


112  THE  SODA  PROCESS 

These  curves  are  characteristic  of  the  soda  process.  The 
difference  between  small  and  large  cooks  is  probably  due  to 
the  difference  in  the  speed  with  which  they  heat  up,  and  in 
fact  by  forcing  the  steaming  in  the  rotary  digester  it  has  been 
found  possible  to  make  the  curve  almost  exactly  duplicate 
curve  A  both  in  form  and  position.  They  also  explain  why 
the  time  factor  is  one  of  minor  importance,  for  the  reaction  is 
one  of  such  great  rapidity  that  over  half  of  the  total  alkali 
consumed  in  a  seven-hour  cook  is  used  up  during  the  first  hour, 
in  spite  of  the  fact  that  during  the  whole,  or  a  great  part,  of 
this  time  the  charge  is  being  brought  up  to  full  pressure. 

Tests  on  Engelmann  spruce  and  red  alder  have  given  results 
which  practically  duplicate  the  curves  of  Fig.  14,  while  Heuser l 
working  on  beech  wood  obtained  very  similar  results.  Chris- 
tiansen,2 on  the  other  hand,  claims  to  have  established  the  fact 
that  there  are  points  at  which  the  reaction  ceases  for  a  while 
and  then  begins  again.  These  pauses  are  of  different  duration 
and  take  place  sooner  or  later  in  the  cook  according  to  local 
conditions.  Some  of  his  cooks  show  two  such  pauses,  some 
one  and  some  not  any,  and  a  careful  study  of  his  work  leads  to 
the  conclusion  that  they  are  probably  due  to  inaccuracies  in 
the  methods  which  he  used  in  sampling  and  analyzing  the 
black  liquors.  It  does  not  seem  reasonable  that  the  reaction 
should  cease  for  a  period  of  half  an  hour  and  then  begin  again 
and  the  author  has  been  unable  to  find  in  the  work  on  poplar 
any  trace  of  such*  pause  which  was  not  readily  explained  by  the 
difficulty  of  obtaining  representative  samples  from  the  black 
liquor  in  the  digester. 

The  methods  of  analysis  used  in  determining  the  rate  of  reac- 
tion make  possible  also  a  study  of  the  relationship  between  the 
caustic  soda  consumed  and  the  yield  of  fibre  produced.  This  was 
investigated  by  us  and  the  results  published 3  in  1 91 2  and  from  this 
paper  the  curves  for  spruce  and  poplar  in  Fig.  15  are  repro- 

1  Heuser:  Wochbl.  Papierfabr.,  44,  2209. 

2  Christiansen:  Uber  Natronzellstoff. 

3  Communications:  Eighth  International  Cong,  of  Appd.  Chem.,  XIII,  p.  265. 


SODA   CONSUMPTION  AND   YIELD 


duced.  It  appears  from  this  that  up  to  the  point  where  14 
per  cent  of  caustic  soda  is  consumed  there  is  merely  a  softening 
of  the  chips  and  almost  no  separation  into  fibres;  between  14 
and  19.5  per  cent  consumption  seems  to  be  the  critical  stage,  for 
between  these  points  the  transition  from  chips,  through  shives 
to  commercially  satisfactory  fibre  takes  place.  Beyond  a  con- 
sumption of  19  per  cent  the  action  appears  to  be  almost  en- 


S 

\ 

CHART  A. 

\ 

s 

^N 

iP 

T3 
1 

X 

s 

\ 

V 

\ 

-PO] 

>lar 

s 

M 

H 

Vv 

? 

\ 

o 

*,-° 

0 

cS 

Spr 

uce 

^ 

"^^ 

*V 

s,. 

fc 

^ 

"N 
^v 

>, 

a 

<D 
O 

^V 

^ 

N 

$ 

X 

w 

\ 

k 

\ 

^ 

\\ 

10     20     30     40     50     60     70 
Percent  Total  Yield 

FIG.  15. 


80 


90    100 


tirely  a  destruction  of  the  cellulose  and  the  decrease  in  yield 
bears  a  constant  ratio  to  the  increase  in  caustic  consumption. 
The  results  from  cooks  of  spruce  chips  give  a  very  similar  curve 
but  the  yield  for  a  given  consumption  of  caustic  soda  is  con- 
siderably lower  than  for  poplar  as  might  be  expected  from  a 
knowledge  of  the  composition  of  the  two  woods.  Studies  along 
this  same  line  by  the  U.  S.  Forest  Service  1  gave  results  which 
seem  to  indicate  that  high  consumption  of  caustic  soda  —  22 

1  U.  S.  Dept.  of  Agriculture,  Bulletin  No.  80. 


THE  SODA  PROCESS 


per  cent  or  more  on  the  weight  of  the  wood  —  may  be  obtained 
without  much  lowering  of  the  yield.  We  believe  that  this 
difference  may  be  due  in  small  part  to  differences  in  the  appara- 
tus and  wood  used  but  that  by  far  the  greater  part  of  it  is  caused 
by  the  analytical  methods  used  by  the  Forest  Service  which 
take  no  account  of  the  occlusion  of  caustic  soda  in  the  precipi- 
tate caused  by  barium  chloride.  It  is  highly  probabje  that  this 
method  of  investigation  could  be  worked  up  into  a  good  con- 
trol test  which  would  largely  eliminate  over-  or  under-cooked 
soda  fibre  and  would  tell  with  reasonable  accuracy  when  the 
desired  quality  of  fibre  had  been  produced. 

Actual  mill  results  in  the  cooking  of  some  Canadian  woods 
are  given  by  De  Cew  l  as  follows: 


Wood 

Specific 
gravity 

Weight 
per 
cord, 
Ibs. 

Soda 
Na2C03 

Yield 

Per 
cent 

Air  dry 
fibre  per 
cord,  Ibs. 

Black  spruce  (Picea  nigra)  

0.41 
0.42 

0-43 
0.425 
0.58 
0.66 
0.64 

2250 
2300 
2350 
2325 
3J9o 
3630 
3520 

900 
950 
800 
800 
800 
850 
850 

40 
38 
44 
44 
42 
40 
40 

1000 

970 

1150 

1135 

1490 

1610 
1560 

Hemlock  (Tsuga  canadensis)  
Poplar  (P.  grandidentata)  

Bass  (Tilia  americana)  

Birch  (Betula  alba}  

Birch  (Betula  lutea)  

Maple  (Acer  rubrum)  

From  other  reliable  sources  the  following  data  have  been 
collected: 


Wood  used 

Weight  per  cord 
bone  dry 

Alkali  per  cord 
as  Na2C03 

Yield  air  dry  fibre 
per  cord 

White  maple  -.'.... 
White  birch  
Gum  and  poplar 

2970 
3091-3218 
3268 

900 
1035-1120 

IO22 

1520 
1460-1592 
1  1  60 

Poplar  . 

2^0 

760 

1250 

Gum  

2976—3040 

920—1138 

1215-1432 

From  soda  mill  records  of  the  cords  of  wood  cooked  and  the 
new  soda  ash  added  to  replace  losses  it  appears  that  184  Ibs.  of 

1  De  Cew:  J.  Soc.  Chem.  Ind.,  1907,  561. 


MODIFIED  PROCESSES  115 

soda  ash  per  cord  suffices  for  poplar  when  the  recovery  is  76 
per  cent,  or  153  Ibs.  with  a  recovery  of  87.5  per  cent.  For  a 
mixture  of  60  per  cent  gum  and  40  per  cent  poplar,  used  during 
a  period  of  six  months,  157  Ibs.  fresh  soda  ash  per  cord  was 
found  to  be  enough  when  the  recovery  was  85.7  per  cent. 

The  best  modern  mills  are  able  to  cook  deciduous  woods  in 
about  four  hours  and  coniferous  woods  in  six  hours.  The  success 
of  these  short  cooks  depends  very  largely  on  vigorous  circula- 
tion and  a  rapid  supply  of  steam.  By  removing  air  from  the 
chips  and  using  superheated  steam  quicker  penetration  of  the 
liquor  is  obtained,  which  also  hastens  the  cooking. 

It  has  been  proposed  at  various  times  to  modify  the  regular 
soda  process  by  the  addition  of  small  amounts  of  other  chemi- 
cals such  as  salt,  sodium  nitrate,  etc.,  and  Schacht l  even  rec- 
ommends cooking  with  a  liquor  consisting  largely  of  sodium  sul- 
phite and  thiosulphate  and  containing  only  enough  caustic  soda 
to  dissolve  silica  and  aluminates.  Careful  tests  have  failed  to 
show  that  salt,  even  when  used  to  the  extent  of  15  per  cent  of 
the  weight  of  the  wood,  exerts  any  protective  action  and  its 
presence  does  not  appear  to  increase  the  yield.  Another  modi- 
fication is  that  of  Freeman  who  proposes  to  carry  out  the  cook- 
ing in  a  reducing  atmosphere  obtained  by  passing  hydrogen 
through  the  digester  until  all  air  is  expelled.  Still  another 
variation  consists  in  saturating  the  chips  with  cooking  liquor 
under  pressure,  drawing  off  the  excess  and  completing  the  cook 
by  steaming  as  usual.  This  is  claimed  to  give  greater  yield 
and  better  fibre  because  of  the  more  uniform  treatment  of  the 
chips. 

The  most  recent  proposal  is  to  add  a  very  small  amount  of 
sulphur — t  about  0.2  per  cent  on  the  weight  of  the  wood  —  to 
the  alkali  during  causticizing  and  it  is  claimed  that  this  will 
materially  increase  the  yield  without  causing  a  serious  nuisance 
by  its  odor.  Very  careful  small-scale  tests  of  this  modification 
have  proved  that  woods  vary  in  their  response  to  the  presence  of 

1  Schacht:  Papier  Ztg.,  1901,  26,  3143. 


n6 


THE  SODA  PROCESS 


sulphur;  some  give  a  larger  yield  while  some  do  not,  but  in 
no  case  is  the  claim  for  10  per  cent  greater  yield  justified.  The 
fibre  produced  in  the  cooks  containing  sulphur  bleaches  more 
easily  in  every  instance.  The  average  yields  for  this  series  of 
tests  are  tabulated  below: 


Kind  of  wood 

Percentage  yield  on  bone  dry  basis 

Without  sulphur 

With  0.2  per  cent  of 
sulphur 

Poplar  

38.9 
36.8 

40-9 
40.6 

41-7 

41.9 
35-7 
40-9 
41.4 
42  .6 

Spruce  

White  birch 

White  maple 

Tulip  tree   . 

It  is  evident  that  each  kind  of  wood  must  be  tested  sepa- 
rately as  the  use  of  sulphur  is  not  equally  beneficial  in  all  cases. 
It  is  probably  due  to  this  reason,  as  well  as  to  the  difficulty  of 
determining , yields  in  actual  mill  operations,  that  at  least  two 
mills  where  the  use  of  sulphur  has  been  tried  out  during  a  period 
of  several  months  report  that  no  increase  in  yield  or  other  ad- 
vantage can  be  noted  and  that  it  tends  to  produce  bad  odors 
even  when  used  in  such  small  amounts  as  0.2  per  cent  on  the 
weight  of  the  wood. 

Numerous  other  modifications  of  the  soda  process  have  been 
proposed  from  time  to  time,  among  which  may  be  mentioned 
Drewsen's  1  plan  for  boiling  wood  chips  in  a  liquor  obtained 
by  adding  10  per  cent  of  quicklime  and  2  to  4  per  cent  of  sul- 
phur to  water;  the  fibre  is  finally  boiled  with  sodium  carbonate 
to  remove  all  sulphur.  Lee  2  proposes,  in  the  case  of  flax  waste, 
boiling  in  a  3  per  cent  solution  of  saccharate  of  lime.  Burton  3 
combines  a  mechanical  treatment  with  the  soda  process  by 
cooking  in  drums  furnished  inside  with  loose  rollers  of  steel  or 
of  steel  filled  with  lead.  This  is  somewhat  similar  to  the 
Muntzing  method  of  treatment4  in  which  the  logs  are  placed 

1  U.  S.  Pat.  996,225,  Jan.  27,  1911.          2  U.  S.  Pat.  713,  116,  Nov.  n,  1902. 
3  Ger.  Pat.  226,912,  Apr.  i,  1909.  4  Paper,  Jan.  20,  1915,  p.  15. 


ALCOHOL  IN  RELIEF  117 

in  the  rotary  digester  without  chipping  and  by  their  rubbing 
action  quickly  separate  the  fibres.  These  are  rapidly  removed 
from  the  sphere  of  action  of  the  liquor  by  pumping  the  latter 
through  a  filter  press  from  which  the  clear  liquor  is  returned  to 
the  digester  to  continue  its  work.  Notably  larger  yields  are 
claimed  for  this  process. 

In  the  case  of  woods  rich  in  turpentine  and  rosin  much  study 
has  been  given  to  the  possibility  of  recovering  these,  while  at 
the  same  time  utilizing  the  wood  as  a  source  of  fibre.  The 
turpentine  can  be  obtained  without  difficulty  in  the  blow-off 
from  the  digesters.  By  a  partial  cook,  followed  by  a  salting 
out  of  the  liquor  with  more  caustic  soda,  Bates  1  has  shown 
that  it  is  possible  to  recover  much  of  the  rosin  in  the  form  of 
sodium  resinate.  Similar  investigations  have  been  conducted 
by  Veitch  and  Merrill 2  and  the  patents  of  Saylor,3  Aktchourine,4 
and  Williamson  5  are  based  on  practically  the  same  principles. 
The  importance  of  such  problems  is  strongly  emphasized  by 
the  estimate  of  the  U.  S.  Government  that  there  are  21,000,000 
cords  of  waste  resinous  woods  in  the  South  annually. 

The  blow-off  from  the  digesters  also  contains,  besides  tur- 
pentine, other  materials  of  an  easily  volatile  nature.  From  the 
relief  of  poplar  cooks  there  have  been  condensed  a  small  amount 
of  oil  and  a  liquid  containing  aldehydes,  ketones,  alcohol,  ace- 
tone, etc.  From  small  scale  cooks  Bergstrom  has  obtained  the 
following  yields  of  alcohol  based  on  the  dry  wood  used. 

Per  cent 

Fichte  (Picea  excelsa) o.  67 

Kiefer  (Pinus  silvestris) o.  67 

Pinus  palustris o.  68 

Pinus  echinata o.  66 

Aspen  (Populus  tremuloides) 0.67 

Birch  (Betula  alba) o.  81 

Gum  (Eucalyptus) o.  83 

1  Bates:  Dissertation,  Columbia  University,  1914. 

2  Veitch  and  Merrill:  Bureau  of  Chem.,  Bull.  No.  159. 

3  Saylor:  Fr.  Pat.  428,678,  April  19,  1911. 

4  Aktchourine:  Fr.  Pat.  433,424,  Aug.  n,  1911. 

6  Williamson:  U.  S.  Pat.  1,025,356,  May  7,  1912. 


n8 


THE  SODA  PROCESS 


At  the  completion  of  a  cook  the  contents  of  a  rotary  digester 
consists  of  material  thoroughly  reduced  to  the  fibrous  condi- 
tion while  that  in  the  stationary  digester  still  retains  very 
largely  the  shape  of  the  original  chips.  Rotary  digesters  are 
discharged  by  blowing  off  pressure  until  the  heads  can  be  re- 


Baffle 


ischarge  Pifee 
FIG.  16.    BLOW  TANK  OR  SEPARATOR 

moved  and  then  emptying  the  contents  by  revolving  the  digester. 
Vertical  digesters  are  emptied  by  blowing  the  entire  charge 
under  full  pressure  through  a  pipe  leading  from  the  bottom  of 
the  digester  to  a  blow  pit  or  some  form  of  steam  separator.  A 
very  satisfactory  device  of  this  sort  is  shown  in  Fig.  16.  The 
stock  enters  tangentially  at  such  high  speed  that  it  hugs  the 


WASH  PITS 


IIQ 


wall  of  the  separator  while  the  steam  escapes  to  the  center  and 
out  through  the  ventilator.  On  blowing  the  charge  the  sud- 
den release  of  pressure  causes  violent  evolution  of  steam  from 
the  moisture  in  the  chips  and  this,  together  with  the  mechanical 
action  of  passing  through  the  discharge  pipe,  causes  complete 
disintegration  into  the  fibrous  state. 

The  blowing  of  a  digester  causes  a  very  large  waste  of  steam. 
It  has  been  estimated  that  in  blowing  a  i5.6-cord  digester  there 
escape  into  the  atmosphere  34,400  Ibs.  of  steam  within  a  period 
of  about  15  minutes.  This  represents  about  41,200,000  British 
thermal  units  and  at  atmospheric  pressure  it  would  occupy  a 
volume  of  925,000  cu.  ft.  The  cost  of  constructing  an  exchange 
heater  which  would  handle  this  enormous  volume  of  steam  in 
such  a  short  time  has  hitherto  been  considered  prohibitive,  and 
very  few  attempts  have  been  made  to  stop  this  waste. 

From  the  separator  the  stock  drops  by  gravity  to  the  wash 
pits.  At  this  point  it  contains  the  fibre,  all  the  alkali  originally 
added,  the  organic  matter  dissolved  during  the  cook  and  a 
large  amount  of  water  both  from  the  liquor  added  and  from 
the  condensed  steam.  The  composition  of  three  samples  taken 
during  the  entire  time  of  discharge  was  found  to  be  as  follows: 


No.  i 

No.  2 

No.  3 

Fibre  (bone  dry)  
Alkali  as  Na2O 

Per  cent 
11.38 
4  I4 

Per  cent 

8-15 
4  .06 

Per  cent 
7-32 

2  .92 

Organic  matter  and  CQz  
Water  

10.76 
73  •  72 

11.31 

76.48 

8.24 
81.51 

The  wash  pits  are  iron  tanks  with  perforated  false  bottoms; 
they  are  of  various  sizes  and  shapes  but  each  should  be  of  suffi- 
cient capacity  to  hold  the  entire  charge  of  a  digester  with  room 
above  the  stock  to  allow  for  flooding  with  water.  The  pits 
supplied  in  one  mill  for  digesters  of  about  15  cords  capacity 
are  19  ft.  6  ins.  in  diameter  by  about  13  ft.  deep  above  the 
false  bottom  which  has  a  2-in.  pitch  toward  the  central  outlet 
to  aid  in  washing  out  the  stock.  One  digester  charge  fills 


120 


THE  SODA   PROCESS 


one  of  these  wash  pits  to  a  depth  of  about  9  to  10  ft.  when 
leveled  off.  In  another  mill  rectangular  tanks  are  recommended, 
the  size  for  5200  to  5300  Ibs.  of  pulp  being  18  X  16  X  5  ft. 
deep. 

The  charge  is  washed  first  by  flooding  with  weak  liquor  from 
a  previous  wash;  the  liquor  taken  off  during  this  period  goes 
to  the  recovery  plant.  The  next  washing  is  with  hot  water, 
which  produces  the  weak  liquor  used  in  the  first  flooding  of  a 
subsequent  cook,  and  the  final  washing  is  with  hot  water  which 
runs  to  the  sewer  as  it  is  too  weak  to  pay  for  evaporation.  The 
approximate  washing  data  for  the  ipi-ft.  tanks  mentioned  above 
are  as  follows: 


First  wash 

Second  wash 

Third  wash 

Time  of  washing,  hours  
Volume  of  liquor  taken  off,  gals. 
Baum6  at  end  

4-7 
18,000-19,000 
5°  at  70°  C. 

5-8 
19,000-20,000 
o°  at  50°  C. 

2-3 

The  net  total  washing  time  is  thus  eleven  to  eighteen  hours 
per  charge  and  the  recovery  of  soda  during  the  washing  has 
been  found  to  be  about  98.5  per  cent.  The  strong  black  liquor 
obtained  by  this  method  contains  about  0.63  to  0.65  Ib.  of 
soda  per  gallon. 

In  some  mills  the  weak  liquor  is  collected  in  a  tank  before 
being  pumped  on  to  the  next  pit,  while  in  other  mills  using  the 
so-called  "cycle  system"  it  is  pumped  directly  from  one  wash 
pit  to  another.  The  advantage  of  the  cycle  system  is  that  it 
requires  less  space  and  produces  stronger  liquor,  while  its  chief 
disadvantages  are  that  it  requires  more  time  to  complete  a 
wash  and  it  is  often  necessary  to  hold  a  pit  with  the  black  liquor 
on  it  to  the  detriment  of  its  bleaching  properties.  Spence  1 
states  that  with  hardwoods  the  liquor  discharged  from  the 
digesters  tests  12°  Be.  at  60°  F.,  while  that  going  to  the  evapo- 
rators tests  9°  Be.  If  the  cycle  system  is  used  the  liquor  to  the 

1  Spence:  Paper,  25  (1919),  134- 


WASHING  BLACK   STOCK  121 

evaporators  would  test  ioj°  Be.  instead  of  9  degs.,  this  differ- 
ence being  equivalent  to  a  saving  in  evaporation  of  46,000 
gals,  per  day  for  a  plant  with  a  daily  capacity  of  100  tons  of 
pulp. 

The  washing  time  depends  very  largely  on  the  depth  of  stock 
which  the  wash  water  has  to  penetrate.  By  dividing  the  digester 
charge  between  two  wash  pits  the  time  of  washing  can  be  very 
greatly  reduced,  but  a  weaker  liquor  is  obtained  and  the  re- 
covery is  not  so  complete  unless  a  much  larger  volume  of  liquor 
is  collected.  This  is  equivalent  to  saying  that  the  greater  the 
drainage  area  allowed  per  ton  of  fibre  per  day  the  more  rapid 
will  be  the  washing.  Beveridge  1  mentions  installations  where 
this  has  varied  from  7!  to  IOT\  sq.  ft.  but  considers  this  far  too 
little  and  recommends  35  sq.  ft.  for  poplar  and  45  to  50  for 
chestnut.  The  kind  of  wood  used  and  the  nature  of  the  cook 
have  an  influence  on  the  speed  of  draining;  hardwoods  drain 
slower  than  northern  poplar  and  overcooking  causes  the  fibre 
to  be  sufficiently  gelatinous  to  drain  slower  than  a  normal 
cook. 

The  temperature  of  the  water  used  also  influences  the  speed 
of  washing,  hot  water  penetrating  the  stock  very  much  faster 
than  cold.  Cold  water,  however,  if  given  time  enough,  will 
remove  impurities  as  completely  as  hot,  the  bleach  required  by 
the  fibre  being  practically  the  same  in  both  cases.  If  the  fibre 
stands  for  any  appreciable  time  in  contact  with  the  black  liquor 
it  appears  to  absorb  coloring  matter  from  the  latter  and  be- 
comes very  hard  to  bleach.  This  is  particularly  true  where  the 
mixture  of  fibre  and  black  liquor  becomes  cold,  twenty-four 
hours'  contact  under  such  conditions  being  enough  to  increase 
the  bleach  required  from  9  to  14  to  15  per  cent.  On  general 
principles  the  stock  should  be  washed  as  soon  as  possible  after 
discharging  from  the  digester  and  access  of  air  or  cooling  of  the 
stock  should  be  avoided  as  far  as  can  be  done  conveniently. 
It  is  particularly  important  that  the  last  traces  of  black  liquor 

1  Beveridge:  Paper,  25  (1919),  198. 


122  THE   SODA  PROCESS 

be  removed  before  the  stock  reaches  the  bleaching  system  since 
even  a  very  small  amount  renders  bleaching  quite  difficult. 

The  results  obtained  in  any  washing  system  depend  on  the 
judgment  of  the  workmen  and  upon  the  care  which  they  use. 
Frequent  tests  are  necessary  and  the  accuracy  of  the  hydrom- 
eter and  the  temperature  at  which  it  is  used  should  be  care- 
fully looked  to.  A  device  which  shows  the  progress  of  the 
washing  by  the  color  of  the  liquor  can  be  installed  at  little 
expense  by  passing  a  small  stream  of  the  liquor  continuously 
through  a  glass  U-tube  beside  which  is  a  gauge  glass  of  the 
same  diameter  and  color.  The  gauge  is  filled  with  black  liquor 
of  the  minimum  strength  which  it  is  desired  to  collect  as  strong 
or  weak  liquor,  as  the  case  may  be,  and  when  the  color  of  the 
washings  is  the  same  as  the  standard  the  collection  of  washings 
of  that  grade  is  discontinued. 

After  washing  the  treatment  of  the  pulp  is  largely  mechanical 
until  it  reaches  the  bleaching  system.  It  is  sluiced  out  of  the 
wash  pits  by  a  heavy  stream  of  water  and  run  through  screens 
to  remove  shives,  uncooked  pieces,  or  knots.  It  goes  next, 
while  in  a  highly  diluted  condition,  over  sand  settlers  which 
are  long,  shallow  troughs  with  crossbars  at  intervals  in  the 
bottom,  and  in  which  sand,  dirt,  cinders,  shives  and  other 
impurities  settle  out.  From  the  sand  settlers  it  goes  to  a  series 
of  extractors  which  remove  a  large  part  of  the  water  and  de- 
liver the  pulp  at  a  proper  concentration  for  bleaching.  During 
these  processes  the  amount  of  water  present  per  pound  of  bone 
dry  fibre  has  been  found  to  be  about  as  follows: 

Lbs. 

In  wash  pits 3.5 

At  knotters 87.  7 

At  centrifugal  screens  and  sand  settlers 123-135 

Entering  bleaching  system 24.  5-27 

Leaks  and  mechanical  losses  of  fibre  should  be  carefully 
looked  for  throughout  this  process.  With  extractors  of  a  type 
similar  to  the  washers  used  on  beating  engines  such  losses 
should  not  amount  to  more  than  i  to  1.5  per  cent  of  the  total 


BLACK  LIQUOR  123 

fibre  and  the  material  lost  will  be  found  to  consist  largely  of 
short  fibres  or  broken  fragments. 

The  pulp  produced  by  the  soda  process  from  poplar  will 
bleach  to  a  good  white  color  with  8  to  12  per  cent  of  bleach, 
while  that  from  coniferous  woods  requires  a  considerably  greater 
amount.  In  some  cases  it  is  not  possible  to  reach  a  high  white 
color  without  a  treatment  so  drastic  as  to  seriously  weaken  the 
cellulose  itself.  For  this  reason  much  of  the  soda  pulp  from 
coniferous  woods  is  used  in  grades  of  paper  which  do  not  require 
a  very  white  fibre. 

Black  Liquor.  It  is  claimed  by  Griffin1  that  the  liquor  in 
the  digester  at  the  end  of  the  cook  is  light  rose  in  color  but 
that  it  immediately  darkens  on  exposure  to  air.  However  this 
may  be,  the  mass  by  the  time  it  reaches  the  wash  pits  is  a  rich 
dark  brown  in  color.  This  is  due  to  the  liquor  and  not  to  the 
fibre  itself  which  when  washed  is  of  a  light  grayish  brown 
shade. 

The  black  liquor  removed  from  the  fibre  during  the  washing 
contains  nearly  all  the  alkali  originally  employed,  together  with 
over  half  the  weight  of  the  wood  used.  Griffin 2  gives  the 
following  analytical  data  for  black  liquor  derived  from  a  soda 
cook  of  poplar  wood,  all  figures  being  based  on  the  weight  of 
total  solids  dried  at  100°  C. 

Per  cent 

Silica  (Si02) o.  1 1 

Oxides  of  iron  and  alumina  (Fe2O3  and  A12O3) o.  02 

Lime  (CaO) o.  05 

Potash  (K2O) o.  69 

Soda  (Na2O) 25. 69 

Carbon  dioxide  (CCfe) .  . 3. 43 

Acetic  acid 9-89 

Organic  matter  extracted  by  naphtha  boiling  below  60°  C 1.56 

Organic  matter  extracted  by  ether 7. 14 

Organic  matter  extracted  by  absolute  alcohol 28.  26 

Organic  matter  extracted  by  water 17. 02 

Total  alkali  by  titration  of  incinerated  residue 44-2$ 

1  J.  Am.  Chem.  Soc.,  1902,  24,  235-238. 

2  Ibid. 


124 


THE  SODA  PROCESS 


Other  analyses  of  black  liquor  from  poplar  showed  the  presence 
of  total  alkali  equivalent  to  65.5  grams  per  liter  of  sodium 
carbonate.  Of  this  total  alkali 

25. 8  per  cent  was  combined  as  acetate 
8.  o  per  cent  was  combined  as  carbonate 

13.3  per  cent  was  combined  as  hydroxide 

13. 5  per  cent  was  combined  with  insoluble  organic  acids 

39. 4  per  cent  was  combined  with  soluble  organic  acids. 

The  proportion  of  caustic  soda  here  present  is  much  less 
than  that  necessary  according  to  Klason  *  who  states  that  40 
per  cent  of  the  total  alkali  must  remain  unused  in  the  black 
liquor  and  that  even  if  the  wood  is  present  in  great  excess  at 
least  25  per  cent  of  the  original  alkali  will  be  found  unconsumed. 
Even  the  difference  between  poplar  and  spruce  seems  hardly 
great  enough  to  account  for  such  differences  as  these.  More- 
over it  has  been  proved  that  if  less  than  9  per  cent  of  caustic 
soda  is  employed  the  wood  uses  it  up  completely,  none  being 
present  in  the  black  liquor.  Even  when  18  per  cent  on  the 
weight  of  the  wood  is  added  fully  90  per  cent  of  it  is  consumed 
and  that  remaining  in  the  liquor  is  reduced  to  a  strength  of  only 
about  1.4  grams  per  liter.  Even  under  actual  working  condi- 
tions the  proportion  of  caustic  remaining  unused  is  much  less 
than  that  claimed  by  Klason,  as  the  following  analyses  of  black 
liquors  from  various  woods  will  show: 


Blacl 

c  liquor 

Caustic  remaining. 

Grams  per  liter 
NaOH 

Per  cent  causticity 

dry  wood 

White  maple 

13    I—  14.    3 

21     I—  21    4 

1  O—   <?  .1 

White  birch  .  .  . 

8  7—21   c 

12  2-28  8 

2  .  Q—  7.7 

Black  gum  

2O    2—22    I 

•2-2      2—  2C     6 

9.8-10.4 

Beech 

10  6—17  6 

1  8    <?—  21     3 

46-48 

Poplar  

6.4-18.1 

15  -3~29  .  i 

3.5-  8.0 

According  to  Griffin  and  Little 2  sodium  formate,  oxalate  and 
acetate  together  with  dark  colored  products  similar  to  ulmic 

1  Christiansen:  Natronzellstoff,  p.  51. 

2  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  164  (1894). 


BLACK  LIQUOR  125 

acid  have  been  recognized  in  the  black  liquor.  Higgins  1  pat- 
ented in  1891  a  method  for  preparing  acetates  from  black  liquor 
by  charring  at  not  over  350  degs.,  but  the  process  has  never 
been  practically  adopted. 

Among  other  processes  for  treating  black  liquor,  Rinman2 
proposes  to  precipitate  the  humus  substances  with  carbonic 
acid  in  the  presence  of  salt  and  after  drying  the  precipitate 
distilling  it  destructively  to  obtain  acetone,  alcohol,  etc.  Tests 
by  the  author  on  liquor  from  poplar  wood  show  that  only  9.2 
per  cent  of  the  total  organic  matter  present. can  be  precipitated 
by  carbonic  acid  and  that  after  very  slight  washing  this1  pre- 
cipitate is  again  readily  dissolved  by  hot  water.  Veitch  and 
Merrill 3  working  with  a  black  liquor  from  Southern  pine  which 
contained  n.i  per  cent  of  organic  matter  in  solution  found  that 
4.9  per  cent  was  precipitated  by  carbon  dioxide  and  a  further 
1.2  per  cent  by  acetic  acid.  Evidently  the  kind  of  wood  used 
very  greatly  influences  the  amount  of  precipitate  obtainable  by 
means  of  carbon  dioxide. 

The  problem  of  the  commercial  utilization  of  black  liquor  is 
a  very  attractive  one  and  many  attempts  have  been  made  to 
obtain  from  it  useful  by-products.  The  humic  matter  precipi- 
tated from  it  by  acids  can  be  used  as  a  sizing  agent  for  paper 
but  the  pinkish  color  which  it  imparts  limits  its  use  to  colored 
papers.  It  has  been  proposed  to  make  a  stain  for  wood  from 
this  organic  matter  and  it  can  also  be  utilized  in  the  manu- 
facture of  brown  sulphur  dyes  or  nitrated  to  form  brown  to 
yellow  dyes.  None  of  these  uses  would  make  much  of  an  im- 
pression on  the  vast  quantities  produced  annually  and  in  all  of 
them  the  recovery  value  of  the  soda  would  be  lost  in  the  process 
of  precipitating  the  organic  matter.  A  more  rational  plan 
would  be  the  destructive  distillation  of  the  black  liquor  in  such 
a  way  that  the  volatile  oils  and  other  materials  could  be  col- 
lected while  the  residual  matter  would  still  contain  all  the  soda 

1  Higgins:  Eng.  Pat.  13,409,  1891. 

2  Rinman:  Soda  Recovery;  Papier  Ztg.,  1911,  3489. 

3  U.  S.  Dept.  of  Agriculture,  Bureau  of  Chem.,  Bull.  No.  159  (1913). 


126  THE  SODA  PROCESS 

in  available  form  for  reuse.  The  products  obtained  from  such 
a  treatment  are  non-condensable  gases,  methyl  alcohol,  acetone, 
aldehydes,  amines,  phenolic  oils,  tar  and  the  retort  residue  con- 
taining the  alkali  and  carbon.  Adding  lime  to  the  charge  be- 
fore distilling  increases  the  amount  of  acetone  in  the  distillate 
while  if  no  alkali  is  added  the  methyl  alcohol  is  present  in  much 
the  greater  amount. 

Recovery  of  Soda.  The  regeneration  of  the  soda  was  not 
attempted  in  the  early  days  of  the  process  but  it  was  soon 
rendered  necessary  by  the  difficulty  in  disposing  of  large  quan- 
tities of  the  waste  liquors  and  by  the  expense  of  repeatedly 
replacing  the  entire  amount  of  alkali.  The  character  of  the 
waste  is  such  as  to  render  recovery  especially  easy  from  a  chemi- 
cal standpoint,  for  about  one-half  of  the  fuel  value  of  the  wood 
is  present  in  the  liquor  and  it  k  in  such  form  that  its  combus- 
tion furnishes  a  large  part  of  the  heat  necessary  to  evaporate 
the  liquors  to  the  point  where  they  may  be  ignited.  After 
burning  the  soda  remains  as  carbonate  in  the  black  ash.  While 
the  process  of  recovery  is  comparatively  simple,  the  necessary 
equipment  is  the  most  expensive  part  of  the  soda  mill  and  its 
efficiency  has  an  important  bearing  on  the  cost  of  production. 

According  to  Griffin  and  Little  l  the  mixture  of  waste  liquor 
and  washings  to  be  treated  usually  tests  from  6°  to  9°  Be.  at 
1 60°  F.  and  in  order  to  maintain  continuous  combustion  it  is 
necessary  to  concentrate  to  at  least  30°  Be.  at  130°  Fv  and  still 
better  to  bring  it  up  to  40°  Be.,  or  higher.  Of  the  very  large 
amount  of  water  which  it  is  necessary  to  evaporate  during  this 
process,  part  comes  from  the  moisture  in  the  chips  and  from 
the  liquor  originally  added,  part  from  the  water  used  in  washing 
and  part  from  the  steam  condensed  during  the  cooking.  This 
latter  item  is  greater  during  cold  weather  and  would  be  some- 
what less  for  stationary  digesters  because  of  the  better  heat 
insulation  in  this  type  of  apparatus. 

Recent  examinations  of  black  liquor  from  poplar  wood  pro- 
duced the  following  data. 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  164  (1894). 


RECOVERY  OF   SODA 


127 


Degrees  Be.  at 
room  tempera- 
ture 

Grains  dry 
matter  per  100 
grams  liquor 

Boiling  points  in  degrees  C.  at  * 

41  inches 
pressure 

20  inches 
pressure 

o  inches 
pressure 

10  inches 
vacuum 

25  inches 
vacuum 

7 
16 

22 
27 
32 

37 

7-8 
18.5 
27.1 
36.6 
46.8 
57-6 

124-5 
128.0 

135-5 

II4-3 
II7-5 

IOI 

90.5 

58.5 

104 

93-o 

62.0 

124.7 

112 

100.9 

69.0 

*  Records  for  pressure  and  vacuum  are  in  inches  of  mercury. 

The  proportions  of  organic  and  inorganic  constituents  in  'black 
liquor  are  indicated  in  the  following  analyses  which  were  made 
on  an  average  sample  of  the  liquor  first  draining  away  from  the 
stock;  this  liquor  tested  i2f°  Be.  at  70°  F. 


Grams  per 
liter 

Per  cent  by 
weight 

Per  cent  on 
total 
solids 

Total  solids  

180.2 

16.4 

Water 

QI7    3 

83  6 

Caustic  soda 

iq    c 

i  8 

10  8 

Total  alkali  as  Na2O 

4Q  -Q 

4-  $ 

27  .  7 

Organic  matter  precipitated  by  HaSO4  

27-3 

2.6 

15-2 

In  practice  the  evaporation  of  black  liquor  is  performed  either 
in  open  pans  or  vacuum  apparatus.  The  Porion  evaporator, 
which  is  representative  of  the  first  class,  consists  of  a  brick 
chamber,  the  lower  part  of  which  forms  a  shallow  reservoir, 
and  through  which  pass  two  cross  shafts  driven  from  the  out- 
side. These  two  shafts  carry  a  series  of  paddles  which  when 
revolved  at  high  speed  throw  the  liquor  into  the  upper  part  of 
the  chamber  in  the  form  of  a  fine  spray.  At  one  end -of  this 
chamber  is  the  calcining  furnace  where  the  final  concentration 
and  incineration  of  the  black  liquor  take  place.  The  burning 
is  assisted  by  a  coal  fire  at  one  end  of  this  furnace  and  all  prod- 
ucts of  combustion  pass  through  the  evaporating  chamber  on 
their  way  to  the  chimney,  thus  heating  and  evaporating  the 
liquor  and  being  themselves  cooled  in  the  process  to  85°  C.  or 


128  THE   SODA  PROCESS 

even  lower.  When  the  liquor  in  the  chamber  has  reached  a 
density  of  26°  to  29°  Be.  it  is  removed  to  a  storage  tank  over 
the  calcining  furnace  from  which  it  is  gradually  fed  into  the 
latter.  This  evaporator  costs  comparatively  little  for  erection 
and  operation  and  it  is  claimed  will  yield  three-quarters  of  a 
ton  of  ash  per  ton  of  coal. 

Enderlein's  evaporator  is  similar  in  principle  but  the  arms 
which  produce  the  spray  are  replaced  with  wrought  iron  discs 
about  six  inches  apart  which  revolve  partly  in  the  liquor  and 
thus  carry  a  thin  film  of  liquid  up  into  the  gases  which  are 
obliged  to  pass  between  the  discs  before  reaching  the  chimney. 
According  to  Beveridge  1  the  fuel  economy  of  this  apparatus  is 
nearly  as  good  as  that  of  multiple  effect  evaporators. 

The  vacuum  or  multiple  effect  evaporators  depend  on  the 
fact  that  the  boiling  point  of  water,  or  other  liquid,  is  lowered 
by  reducing  the  pressure  under  which  it  boils.  The  boiling 
temperatures  for  black  liquor  already  given  in  the  accompanying 
table  illustrate  this,  and  these  will  be  found  to  follow  very 
closely  the  boiling  points  of  water  under  similar  conditions. 
Apparatus  working  on  this  principle  is  so  constructed  that  the 
steam  from  the  liquid  evaporated  in  the  first  section,  or  "  effect," 
is  used  to  boil  that  in  the  second  effect,  this  being  kept  under 
enough  lower  'pressure  so  that  active  ebullition  takes  place.  The 
steam  from  the  second  effect  in  turn  boils  the  liquor  in  the  third 
effect  and  so  on  through  the  system  which  may  consist  of  three 
to  five  effects.  The  only  necessity  for  heat  from  outside  sources 
is  therefore  in  the  first  effect  in  which  the  liquor  is  raised  from 
the  entering  temperature  to  the  temperature  of  ebullition  at  the 
pressure  in  this  effect.  The  pressure  in  the  first  effect  varies 
greatly  in  different  mills  and  with  different  types  of  apparatus. 

One  of  the  evaporators  most  frequently  used  in  soda  pulp 
mills  is  the  Yaryan  in  which  the  liquor  passes  back  and  forth 
through  the  tubes  and  finally  is  discharged  against  baffle  plates 
in  a  separating  chamber.  The  tubes  are  3  ins.  in  diameter 

1  Beveridge:  Paper  Makers'  Pocket  Book,  p.  106. 


RECOVERY  OF  SODA 


129 


. 


FIG.  17.    Y ARYAN  EVAPORATOR 
Courtesy  of  Mr.  Chas.  Ordway 


130  THE  SODA  PROCESS 

and  12  ft.  long  and  as  five  tubes  form  a  unit  the  liquor  travels 
60  ft.  before  it  is  discharged.  From  this  chamber  the  steam 
passes  into  the  shell  of  the  next  effect  while  the  liquor  goes  to 
the  tubes.  The  vacuum  is  maintained  by  means  of  a  con- 
denser and  pump  and  the  strong  black  liquor  is  removed  from 


FIG.  18.    Y ARYAN  EVAPORATOR  TEED  END  OF  ONE  EFFECT 
Courtesy  of  Mr.  Chas.  Ordway 

the  last  effect  by  another  pump  which  usually  discharges  it 
into  tanks  over  the  furnaces.  The  efficiency  of  the  Yaryan  is 
said  to  be  due  in  part  to  the  rapid  motion  of  the  liquor  through 
the  tubes  and  the  more  rapid  absorption  of  heat  which  results. 
The  time  required  for  liquor  to  pass  through  all  the  effects  is 
but  a  few  minutes,  and  as  only  a  small  amount  of  liquor  is 
present  at  any  one  time  the  evaporator  can  be  started  and 
stopped  very  quickly. 


EVAPORATORS 


Several  types  of  Yaryan  evaporators  are  on  the  market.  Fig. 
17  shows  a  horizontal  evaporator  in  general  view  and  a  section 
of  one  effect,  while  Fig.  18  shows  the  feed  pipes  and  the  return 
bends  of  part  of  the  coils.  It  is  to  be  noted  that  uniform  feed 
for  all  coils  is  insured  by  bringing  the  feed  pipes  all  down  to  one 
level. 

In  other  types  of  multiple  evaporators  the  positions  of  the 
steam  and  liquor  are  reversed,  the  steam  being  in  the  tubes 


Internal 
LighT* 


Vapor  Outlet 


Peeph 


FIG.  19. 


D-rain 


Washout 

ZAREMBA  EVAPORATOR  VERTICAL  CROSS  SECTION  OF  ONE  EFFECT 

Courtesy  of  Zaremba  Company 


while  the  liquor  to  be  concentrated  flows  over  them  by  gravity 
in  a  thin  film.  The  Zaremba  evaporator,  a  cross  section  of 
one  effect  of  which  is  shown  in  Fig.  19,  is  of  this  type.  This 
evaporator  is  giving  good  service  on  black  liquor  and  in  one 
installation  a  four-effect  evaporator  with  bodies  14  ft.  in  diam- 
eter is  handling  350,000  gals,  daily. 


132  THE  SODA  PROCESS 

Numerous  tests  on  both  types  of  evaporators  have  proved 
that  an  evaporation  of  3  to  3^  Ibs.  of  water  from  and  at  212°  F. 
can  be  maintained  under  ordinary  working  conditions,  while 
if  the  heat  necessary  to  bring  the  liquor  to  the  boiling  point  is 
considered  the  evaporation  would  be  somewhat  less,  say  2.6  to 
2.9  Ibs.  of  water  per  pound  of  steam.  Assuming  an  evapora- 
tion of  8J  Ibs.  of  water  per  pound  of  coal  under  the  boilers  the 
patentees  of  the  Yaryan  evaporator  claim  that  a  double  effect 
will  evaporate  16  Ibs.,  a  triple  effect  23!  Ibs.  and  a  quadruple 
effect  30!  Ibs.  of  water  per  pound  of  coal.  Tests  under  ordi- 
nary running  conditions  have  shown  an  evaporation,  for  a 
three-effect  Yaryan,  of  18  to  20  Ibs.  of  water  per  pound  of  coal 
on  the  above  assumption. 

After  evaporation  the  liquor  goes  to  a  storage  tank  and  thence 
to  the  incinerating  furnace.  This  furnace  consists  of  a  revolv 
ing,  cylindrical  shell  lined  in  such  a  way  that  the  interior  is 
somewhat  conical  with  the  large  end  toward  the  fire  box.  Mod- 
ern furnaces  are  quite  generally  about  20  ft.  long  and  9  ft.  out- 
side diameter,  but  some  are  built  as  much  as  30  ft.  long.  The 
lining  is  of  ordinary  hard-burned  red  brick  and  is  about  15  ins. 
thick  at  one  end  and  9  at  the  other.  The  placing  of  pieces  of 
cast  iron  at  intervals  helps  to  resist  wear;  the  links  of  old  chain 
grates  placed  edgewise  have  proved  very  good  for  this  purpose. 
The  furnace  is  mounted  on  wheels  and  fitted  with  a  gear  by 
which  it  is  caused  to  turn  at  a  speed  of  one  to  three  revolutions 
per  minute  according  to  the  condition  of  the  liquor  supply. 

At  the  discharge  end  of  the  -furnace  there  is  a  fire  box, 
mounted  on  wheels  which  rest  upon  rails  so  that  the  whole  can 
be  drawn  back  out  of  the  way  when  the  furnace  proper  needs 
repairs.  This  fire  box  is  arranged  to  burn  coal,  wood  waste,  gas 
or  oil  according  to  local  conditions.  It  is  usually  impossible  to 
get  a  very  accurate  estimate  of  the  fuel  burned  per  ton  of  ash 
because  the  use  of  waste  material  is  so  general.  In  one  mill 
where  both  wood  and  coal  were  burned  the  amount  of  the  latter 
was  only  120  Ibs.  per  ton  of  ash  produced.  During  a  test  on 
a  2o-ft.  furnace  burning  all  coal  with  a  moisture  content  of  2.33 


LEACHERS  133 

per  cent,  and  running  liquor  at  38°  Be.,  the  coal  burned  per 
ton  of  ash  produced  was  117  Ibs.,  while  under  similar  conditions 
325  Ibs.  of  shavings  with  a  moisture  content  of  39  per  cent  were 
required. 

Fig.  20  shows  diagrammatically  the  arrangement  of  a  modern 
recovery  plant  with  its  rotary  furnace,  fire  box  and  boiler  set- 
ting for  the  recovery  of  waste  heat  from  the  incinerator.  Such 
a  boiler  will  produce  a  very  considerable  part  of  the  steam  neces- 
sary for  the  evaporation  of  the  black  liquor.  In  one  plant  the 
boiler  over  a  furnace  burning  21  tons  of  ash  per  day  developed 
150  to  1 60  horse  power  when  it  was  in  good  condition. 

The  strong  black  liquor  which  enters  the  back  end  of  the 
furnace  is  not  yet  concentrated  enough  to  support  its  own 
combustion.  As  it  works  forward  in  the  furnace  it  loses  water 
and  finally  takes  fire,  the  organic  compounds  are  destroyed 
and  it  is  finally  discharged  in  a  glowing  condition  containing 
practically  only  carbon  and  sodium  carbonate.  If  it  is  well 
burned  there  is  at  most  a  slight  blue  flame  to  the  discharged 
ash,  but  if  the  furnace  is  pushed  a  little  too  hard  the  ash  may  be 
under-burned  in  which  case  it  may  show  considerable  yellow 
flame  even  after  it  is  dumped  into  the  leaching  tanks.  Under 
ordinary  conditions  a  2o-ft.  furnace  operated  by  experienced 
men  will  produce  30  to  33  tons  of  ash  in  twenty-four  hours 
and  under  exceptionally  favorable  conditions  the  product  may 
go  as  high  as  42  to  43  tons.  The  lining  of  such  a  furnace  will 
not  last  much  over  six  months  and  if  it  is  pushed  harder  than  it 
should  be  it  will  need  repairs  rather  sooner. 

The  recovered  ash  in  the  soda  process  will  contain  65  to  80 
per  cent  of  sodium  carbonate  according  to  the  care  with  which 
it  has  been  burned.  There  are  small  amounts  of  iron,  alumina, 
lime,  sulphur  and  silica  derived  from  various  sources  and  about 
1 8  to  22  per  cent  of  carbon. 

From  the  furnaces  the  ash  goes  to  some  form  of  leaching 
device,  either  open  tanks  or  closed  tanks  to  which  pressure  can 
be  applied.  In  the  open  tanks  it  is  first  flooded  with  weak 
liquor  from  below  in  order  to  avoid  causing  explosions  when 


134 


THE   SODA  PROCESS 


LOSSES  135 

water  comes  in  contact  with  the  glowing  ash.  The  washing 
is  carried  out  systematically  in  order  to  produce  a  leach  liquor 
of  good  strength  and  at  the  same  time  lose  as  little  soda  as 
possible.  The  closed  tank  system  saves  floor  space  and  time 
in  leaching  but  much  care  is  necessary  in  order  to  avoid  explo- 
sions. There  seems  to  be  little  to  choose  between  the  two 
systems  so  far  as  operating  efficiency  is  concerned. 

Black  Ash  Waste.  This  material,  which  remains  in  the  leach- 
ing tanks  at  the  end  of  the  washing,  consists  of  light  porous  car- 
bon contaminated  with  small  amounts  of  impurities.  Because 
of  its  physical  condition  it  is  very  difficult  to  remove  the  water 
it  contains.  When  drained  as  much  as  possible  in  the  leach 
tanks  it  still  contains  80  to  85  per  cent  of  water,  even  in  the  top 
layers  which  are  driest.  The  use  of  a  centrifugal  machine  will 
not  reduce  this  moisture  below  65  to  68  per  cent  and  beyond 
this  point  it  can  be  dried  only  by  the  application  of  heat. 

The  following  analysis  gives  an  idea  of  the  composition  of  this 
waste.  The  sample  had  been  thoroughly  dried  and  then  exposed 
to  the  air. 

Per  cent 

Moisture,  H2O 6. 06 

Sodium  carbonate,  Na2CO3 2.51 

Calcium  carbonate,  CaCOs 1. 17 

Sodium  sulphide,  Na2S o-  37 

Magnesia,  MgO o.  34 

Iron  and  alumina,  Fe2Oa  and  A^Os o.  26 

Silica,  SiC>2 o.  17 

Calcium  sulphate,  CaSO4 o.  07 

Carbon  by  difference,  C 89. 05 

No  use  for  this  material,  which  will  even  begin  to  take  care 
of  the  amount  made,  has  ever  been  developed.  The  most 
promising  field  seems  to  be  as  a  fuel,  since  the  heating  value  of 
the  dried  waste  is  14,000  to  14,500  B.T.U. 

Losses.  The  chief  loss  to  which  attention  should  be  paid  is 
that  of  soda.  This  occurs  at  numerous  points,  all  of  which  should 
be  subjected  to  careful  scrutiny. 

The  loss  in  the  lime  mud  should  be  checked  by  routine  analy- 
ses. These  will  indicate  whether  the  process  is  being  run  care- 


136  THE  SODA  PROCESS 

fully  and  may  prove  that  a  different  lime  can  be  used  which 
will  permit  better  settling  and  cleaner  washing.  The  loss  in 
the  waste  lime  sludge  will  be  about  2.0  per  cent  of  its  dry  weight 
under  average  conditions. 

The  loss  in  washing  out  the  black  liquor  from  the  fibre  may 
be  studied  by  analyses  and  volume  measurements  of  the  final 
washings.  Such  studies  indicate  that  under  normal  conditions 
this  loss  will  amount  to  i  to  1.5  per  cent  of  the  total  soda  used 
in  the  digesters.  There  is  also  a  loss  due  to  the  presence  of  a 
small  amount  of  soda  in  the  washed  fibre;  this  has  been  found 
to  be  about  1.5  per  cent  of  the  soda  used.  Under  abnormal 
conditions,  as  when  the  recovery  plant  cannot  keep  up  with 
the  wash  pits,  there  is  likely  to  be  a  much  greater  loss  in  the 
final  wash  water. 

The  losses  in  burning  the  black  ash  are  hard  to  determine 
because  the  process  is  a  continuous  one  and  reliable  measure- 
ments of  the  materials  going  to  and  coming  from  the  furnaces 
are  seldom  made.  Moreover  the  loss  is  chiefly  in  material 
carried  up  the  stack  mechanically  or  because  of  a  slight  vola- 
tilization of  soda.  Spence  1  has  studied  the  loss  up  the  flues 
and  gives  the  soda  lost  per  twenty-four  hours  as  follows  for 
different  sizes  of  incinerators. 

Lbs. 

14-foot  rotaries 450-1000 

i6-foot  rotaries 650-1300 

3o-foot  rotaries 2500-4000 

In  the  leaching  of  the  black  ash  there  is  a  loss  of  soda  which 
may  run  from  a  few  tenths  of  a  per  cent  up  to  four  or  five  per  cent 
for  unsatisfactory  conditions.  While  it  would  seem  an  easy 
matter  to  determine  this  loss  it  has  proved  to  be  a  very  difficult 
proposition  because  the  nature  of  the  material  and  the  way  it 
is  handled  make  it  almost  impossible  to  obtain  a  fair  sample. 

Tests  and  Analyses  for  the  Soda  Process.  The  analytical 
work  necessary  for  the  control  of  the  soda  process  is  of  a  com- 
paratively simple  nature.  The  materials  which  should  be  tested 
1  Spence:  Paper,  1919,  619. 


TESTS  AND  ANALYSES  137 

either  regularly  or  at  intervals  are  the  cooking  liquor  and  black 
liquor,  soda  ash,  lime,  lime  mud,  black  ash  and  black  ash  waste. 
The  cooking  liquor  contains  caustic  soda  as  the  essential  in- 
gredient, but  it  also  contains  soda  ash  and  in  some  cases  salt, 
which  renders  its  valuation  by  a  simple  hydrometer  test  some- 
what misleading.  The  actual  grams  per  liter  of  caustic  soda 
should  be  determined  by  titrating  10  c.c.  with  normal  acid 
using  first  phenolphthalein  and  finally  methyl  orange  as  indi- 
cator. The  methyl  orange  shows  the  total  alkali  while  the 
phenolphthalein  shows  all  the  caustic  soda  and  half  the  car- 
bonate. Twice  the  difference  between  the  two,  subtracted 
from  the  methyl  orange  reading,  gives  the  acid  to  neutralize 
the  caustic  soda  and  this  multiplied  by  4  gives  the  grams  per 
liter  of  NaOH.  The  causticity  of  the  cooking  liquor  should 
also  be  recorded;  this  is  obtained  by  dividing  the  cubic  centi- 
meters of  acid  required  for  the  caustic  soda  by  the  volume 
necessary  for  the  total  alkali.  Probably  most  practical  mill 
men  would  say  that  the  Baume  test  is  the  only  one  necessary 
but  for  the  reasons  given  above  this  test  alone  may  lead  to 
entirely  incorrect  conclusions. 

Soda  ash  is  ordinarily  one  of  the  purest  of  commercial  chemi- 
cals yet  it  is  desirable  to  test  it  occasionally  when  received  and 
if  it  is  stored  in  bulk  it  is  sometimes  necessary  to  determine 
the  amount  of  moisture  which  it  has  taken  up.  For  moisture 
a  representative  sample  of  i  to  2  grams  is  accurately  weighed 
into  a  platinum  crucible  and  dried  for  three-quarters  of  an  hour 
over  a  gas  flame  which  is  so  adjusted  that  the  bottom  of  the 
crucible  just  shows  a  faint  redness  when  shielded  from  strong- 
light.  After  cooling  in  a  desiccator  it  is  quickly  reweighed,  the 
loss  being  calculated  as  percentage  of  moisture.  For  the  de- 
termination of  alkali  present  the  dried  sample  is  dissolved  in 
water  and  titrated  with  normal  acid  using  methyl  orange  as 
indicator.  The  percentage  of  sodium  carbonate  in  the  original 
sample  is  calculated  by  the  following  formula 

C.  C.  acid  X  0.053 

Weight  of  sample  before  drying 


138  THE  SODA  PROCESS 

The  lime  used  in  causticizing  should  be  regularly  tested  in 
order  to  see  that  its  quality  is  kept  up  to  a  reasonable  standard. 
A  chemical  analysis  will  not  necessarily  show  what  results  it 
will  give  in  practice  but  a  simple  causticizing  test  made  under 
conditions  similar  to  those  of  actual  work  will  give  very  valu- 
able information.  From  each  car  of  lime  received  as  fair  a 
sample  as  possible  should  be  taken  by  going  all  over  the  car 
and  taking  portions  from  the  top,  middle  and  bottom  of  the 
load.  This  should  be  selected  to  represent  both  the  fine  and 
the  coarse  material  and  as  soon  as  the  entire  sample  is  taken  it 
should  be  crushed  and  quartered  down  as  rapidly  as  possible 
to  avoid  the  absorption  of  moisture.  From  this  final  sample  a 
weighed  amount  is  taken  and  boiled  for  exactly  one  hour  with 
water  and  a  weighed  amount  of  dry  soda  ash  which  is  in  excess 
of  the  amount  the  lime  can  causticize.  The  amount  of  water 
used  is  so  taken  that  the  final  solution  at  the  end  of  the  test 
is  about  the  strength  of  that  used  in  practice.  After  the  boiling 
is  completed  the  sludge  is  allowed  to  settle  and  the  clear  liquor 
is  titrated  with  both  phenolphthalein  and  methyl  orange  as  in 
the  case  of  cooking  liquor.  Knowing  the  causticity  from  this 
titration  and  the  weight  of  soda  ash  taken  the  amount  of  lime 
required  to  causticize  100  Ibs.  of  dry  soda  ash  may  be  calculated 
by  this  formula: 

Weight  of  lime  used  X  100 
Per  cent  causticity  X  weight  of  soda  ash  used 

The  settling  quality  of  the  lime  may  be  ascertained  in  this 
same  test  by  taking  a  sample  of  the  rapidly  boiling  mixture 
just  at  the  end  of  the  test  and,  without  giving  it  time  to  settle, 
filling  a  100  c.c.  graduate  just  to  the  upper  mark.  By  noting 
the  cubic  centimeters  of  clear  liquor  at  fixed  time  intervals  the 
relative  settling  qualities  of  the  various  limes  can  be  compared. 

The  lime  mud  which  settles  in  the  causticizing  and  washing 
tanks  is  generally  a  waste  product  and  in  order  to  see  that 
too  much  caustic  soda  is  not  thrown  away  it  should  be  tested 
at  intervals  for  the  amount  of  alkali  present.  A  representative 
sample  of  the  dried  mud  is  weighed  out,  placed  in  a  small  por- 


TESTS   AND   ANALYSES  139 

celain  dish  and  moistened  with  strong  ammonium  carbonate 
solution.  It  is  next  evaporated  to  dryness,  heated  over  a  low 
flame  until  no  odor  of  ammonia  can  be  noticed,  and  finally 
leached  out  repeatedly  with  boiling  distilled  water  until  all  the 
soluble  alkali  is  removed.  The  combined  leachings  are  then 
titrated  with  standard  acid,  using  methyl  orange  as  indicator, 
and  the  results  calculated  to  precentage  of  alkali  based  on  the 
dry  lime  mud. 

In  the  case  of  black  liquor  it  is  at  times  desirable  to  know 
the  strength  both  in  total  alkali  and  in  free  caustic  soda.  For 
total  alkali  evaporate  a  measured  volume  to  dryness  in  a  plati- 
num dish  and  ignite  over  a  flame  till  the  organic  matter  is  com- 
pletely carbonized.  Cool,  extract  several  times  with  hot  water 
and  pour  the  extracts  through  a  small  platinum  cone.  Put  the 
cone  in  the  dish  together  with  the  residual  wet  carbon,  cover 
with  a  filter  paper  which  just  fits  inside  the  dish  and  quickly 
ignite  over  a  gas  flame.  The  filter  paper  prevents  loss  by 
spattering  and  enables  the  carbon  to  be  burned  off  without 
waiting  for  it  to  be  dried  first.  Again  cool  and  extract  with 
hot  water,  add  the  extract  to  the  first  and  titrate  with  acid  in 
the  presence  of  methyl  orange.  Calculate  the  results  to  grams 
of  sodium  carbonate  per  liter  or  pounds  per  gallon. 

For  the  determination  of  free  caustic  soda  in  black  liquor 
add  25  c.c.  of  the  latter  to  400  c.c.  of  water  and  15  c.c.  of  barium 
chloride  solution  (400  grams  per  liter)  in  a  beaker.  Titrate 
directly  with  standard  acid  using  a  dilute  solution  of  phenol- 
phthalein  on  a  spot  plate  as  an  indicator.  The  acid  should  be 
added  quite  slowly  and  the  end  point  may  be  considered  as 
that  point  at  which  no  pink  color  develops  within  two  minutes 
after  mixing  one  or  two  drops  of  the  liquid  with  the  indicator. 
Owing  to  the  presence  of  soluble  coloring  matter  and  to  the 
precipitate  thrown  down  by  the  barium  chloride  the  end  point 
is  not  very  sharp  but  with  a  little  practice  it  is  fairly  easy  to 
get  concordant  results.  A  sharper  end  point  is  obtained  by 
filtering  off  or  settling  out  the  barium  precipitate  and  using 
only  the  clear  liquor,  but  this  introduces  a  distinct  error  due 


140  THE   SODA  PROCESS 

to  the  loss  of  the  caustic  soda  occluded  by  the  precipitate.  In 
the  method  outlined  above  this  is  kept  within  the  sphere  of 
action  of  the  acid  and  more  accurate  results  are  obtained. 

Analyses  of  black  ash  and  black  ash  waste  are  usually  con- 
fined to  simple  determinations  of  the  amount  of  soluble  alkali 
present.  In  the  case  of  black  ash  this  may  be  leached  out  with 
hot  water  and  titrated  as  usual  in  the  presence  of  methyl  orange. 
With  black  ash  waste  the  volume  of  carbon  is  relatively  so 
large  that  it  is  well  to  burn  off  most  of  it  in  a  platinum  dish 
before  attempting  to  leach  out  the  soda. 


CHAPTER  V 
THE  SULPHATE  PROCESS 

The  sulphate  process  is  similar  to  the  soda  process  in  that  the 
cooking  liquor  is  alkaline,  but  it  differs  from  it  by  replacing  the 
alkali  lost  with  sodium  sulphate  instead  of  soda  ash.  In  rare 
cases  both  are  used  but  the  sulphate  is  always  in  the  greater 
amount  and  it  is  from  the  use  of  this  material  that  the  process 
gets  its  name.  Actually  it  is  a  misnomer,  and  it  would  be  better 
to  call  it  the  sulphide  process  because  of  the  important  part 
played  by  sodium  sulphide  in  the  cooking  liquor.  This  sulphide 
is  derived  from  the  sulphate  by  reduction  in  the  recovery  of  the 
alkali  and  it  is  this  feature  which  introduces  the  greatest  deviation 
from  the  soda  process. 

There  is  more  or  less  confusion  in  the  use  of  the  terms  "  sul- 
phate" and  "kraft"  as  applied  to  the  process  and  products. 
Sulphate  may  be  considered  as  a  general  term  applying  to  any 
cooking  process  in  which  the  loss  of  alkali  is  made  up  by  adding 
sodium  sulphate,  while  kraft  is  that  subdivision  of  the  sulphate 
process  in  which  the  pulp  is  intentionally  undercooked  in  order 
to  produce  very  strong  stock.  The  products  of  the  sulphate 
process  vary  according  to  the  cooking  conditions  from  the  dark 
brown,  unbleachable  kraft  fibre  to  a  soft,  easy  bleaching  stock. 
The  latter  may  be  used  in  making  white  papers  where  it  gives 
a  soft,  pliable  sheet  in  comparison  with  the  harder  and  more 
rattly  paper  from  sulphite.  The  principal  use  of  the  sulphate 
process  however  is  in  the  preparation  of  kraft  stock. 
^The  sulphate  process  has  two  chief  advantages  over  the  sul- 
phite process:  the  chemicals  used  can  be  recovered  and  the 
wood  used  may  be  of  a  highly  resinous  nature.  It  is  this  second 
fact  which  gives  the  process  its  widest  application.  As  compared 
\  141 


142  THE  SULPHATE  PROCESS 

with  the  soda  process  it  gives  somewhat  higher  yields  and  employs 
a  cheaper  source  of  alkali.  Its  one  disadvantage  lies  in  the 
extremely  disagreeable  odors  due  to  the  organic  sulphur  com- 
pounds formed  during  cooking  and  recovery.  This  has  been 
found  serious  enough  to  limit  its  use  to  sparsely  inhabited  local- 
ities.^' 

As^the  process  is  an  alkaline  one  there  is  no  appreciable  action 
upon  the  digester  plates  and  it  is  not  necessary  to  use  any  lining. 
The  equipment  used  is.  very  similar  to  that  for  the  soda  process 
though  the  digesters  are,  as  a  rule,  smaller,  yielding  from  two  to 
three  tons  of  pulp  per  charge.  There  is  a  tendency  in  Europe 
towards  the  use  of  digesters  which  "rotate  on  their  short  axes. 
The  sizes  of  these  are  variously  reported  as  18  to  45  cubic  meters 
capacity  (635  to  1590  cu.  ft.).  The  digesters  should  always  be 
welded  and  not  riveted,  as  the  latter  are  bound  to  develop  leaks 
from  the  continual  expansion  and  contraction  to  which  they  are 
subjected. 

The  cooking  process  employed  depends  on  whether  kraft  fibre 
or  easy  bleaching  stock  is  to  be  produced.  For  kraft  fibre  in 
which  a  dark  color  is  desired  a  portion  of  the  cooking  liquor  is 
made  up  of  black  liquor  containing  practically  no  caustic  soda. 
The  proportion  of  this  black  liquor,  as  might  be  expected,  varies 
considerably,  some  mills  using  as  little  as  27  per  cent  while  in 
others  it  amounts  to  nearly  60  per  cent  of  the  total  liquor.  The 
volume  of  liquor  used  is  about  45  to  50  per  cent  of  the  capacity 
of  the  digester  and  it  tests  8°  to  1 2°  Be.  at  60°  C.  if  indirect  heat- 
ing is  employed  or  18°  to  23°  Be.  .when  steam  is  blown  into  the 
charge.  Beveridge1  states  that  the  total  volume  of  liquor 
should  not  be  less  than  150  cu.  ft.  per  2000  Ibs.  of  air-dried 
pulp  produced,  or  per  i  .60  cords  of  wood.  The  relative  volumes 
of  white  and  black  liquor  would  then  depend  on  the  strength  of 
the  former  as  delivered  by  the  causticizing  system,  any  excess 
over  the  volume  of  white  liquor  necessary  to  give  the  required 
amount  of  alkali  being  made  up  by  black  liquor.  The  alkali 
required  in  making  kraft  fibre  is  said  to  be  640  Ibs.  per  ton  of  pulp. 

1  Beveridge:  Paper,  1918,  22,  21. 


RELATIVE  VALUE  OF  ALKALIS 


The  cooking  time  is  from  i|  to  6  hours  and  the  steam  pressure 
employed  varies  from  no  Ibs.  to  135  Ibs.,  the  highest  pressure 
being  held  for  only  i|  to  2  hours.  In  practice  it  is  seldom  neces- 
sary to  cook  at  more  than  no  Ibs.  pressure.  For  easy  bleaching 
fibre  no  black  liquor  is  used  and  if  the  cooking  liquor  has  to  be 
diluted  water  only  is  employed.  The  other  cooking  conditions 
are  about  the  same  as  they  are  for  kraft  fibre. 

A  modification  of  the  usual  cooking  process  is  that  proposed 
by  Ungerer  1  in  which  the  cooking  liquor  is  passed  through  a 
series  of  digesters  until  exhausted.  The  original  installations 
were  of  small  digesters  and  the  process  has  never  been  very 
extensively  used.  The  chief  trouble  seems  to  have  been  in  keep- 
ing the  liquor  heaters  in  repair,  while  the  advantages  claimed 
were  more  uniform,  stronger  and  easier  bleaching  fibre.  The  fol- 
lowing figures  2  show  the  strength  of  the  various  constituents  in 
a  definite  quantity  of  the  liquor  as  it  passes  the  digesters  in  series. 


Digester 

Total  soda  as 
Na2O 

Soda  combined 
with  organic 
matter 

Soda  as  NaOH 

Soda  as  Na2CO3 

2 

874 

251 

298 

325 

3 

729 

543 

31 

155 

4 

657 

579 

22 

56 

611 

552 

9 

50 

6 

605 

558 

3 

44 

7 

598 

582 

o 

16 

From  experiments  in  the  Forest  Products  Laboratory  3  it  has 
been  proved  that  increasing  the  amount  of  either  the  caustic 
soda  or  the  sodium  sulphide  decreases  the  yield  and  that  the 
former  has  about  twice  as  much  influence  as  the  latter..  The 
carbonate  and  sulphate  of  sodium  are  apparently  without  effect 
on  the  wood.  This  has  been  confirmed  by  observations  under 
actual  working  conditions  and  Beveridge  4  expresses  the  opinion 

1  Ungerer:  Papier  Ztg.,  22  (94),  3360. 

2  Knosel:  Papier  Ztg.,  22  (97),  3470. 

3  Wells:  Paper,  Sept.  24,  1913,  p.  15. 

4  Beveridge:  Paper,  1918,  22,  21. 


144 


THE  SULPHATE  PROCESS 


that  the  caustic  soda  unites  with  the  organic  matter  first  and 
when  exhausted,  or  nearly  so,  the  sulphide  comes  into  play. 

The  composition  of  sulphate  cooking  liquor,  according  to 
several  different  authorities,  is  given  below  in  tabular  form,  the 
quantities  of  the  various  substances  being  expressed  as  grams  per 
liter. 


Authority 

Na»CO, 

NaOH 

Na,S 

NatSO, 

Na,S04 

Deg.  E6 

M.  Mullcr  *  • 

24.00 

45  -°o 

13  .00 

2.OO 

14.00 

Schacht  *  

36.00 

80.60 

IS  -So 

7.2S 

I  $  .  IO 

17.8 

Schacht  *  
Heuser  t  

45-05 
7.48 

77.80 
61.80 

11.25 

25  .12 

8.19 
3.78 

12.  l8 

4.52 

18.5 

Klein  J.  . 

IS    OO 

62  oo 

22    OO 

3    OO 

IO.OO 

55-oo 

30.00 

3-oo 

5-oo 

*  Kirchner:  Das  Papier,  p.  109. 

I  Heuser:  Papier  Ztg.,  1910,  p.  1511. 
Klein:  Papier-Fabr.,  1914.  p.  628. 


From  the  investigations  of  E.  Heuser 1  on  beechwood  it  appears 
that  comparatively  little  sodium  sulphide  is  used  up  during  the 
process.  The  following  table  shows  the  strength  of  the  cooking 
liquor  used  in  three  of  his  cooks  and  the  percentages  of  the  indi- 
vidual constituents  consumed. 


i 

2 

3 

NaaS  added  in  grams  per  liter  

IQ  .  SO 

24.7O 

21  .40 

NaOH  added  in  grams  per  liter  
NajCOs  added  in  grams  per  liter 

27-75 

18  oo 

48.55 
22    OO 

28.20 
9QO 

Percentage  consumption  of  NajS 

7   QS 

IS    60 

7    OO 

Percent  ii<v  (.•on^umpt  ion  of  XaOlI 

6q  80 

SI    2O 

6^    80 

Percentage  consumption  of  NasCOs 

3Q   OO 

6  40 

2    80* 

*  Percentage  Increase 

In  all  three  cooks  the  Na2SO4  present  increased  very  slightly 
during  the  cook. 

The  materials  necessary  to  produce  one  ton  (2000  Ibs.)  of 
sulphate  pulp  vary  quite  widely  in  different  mills;  the  following 
seem  to  be  the  limiting  values: 

1  Heuser:  Wochbl.  Papier-Fabr.,  1913,  p.  2209. 


YIELD   OF   FIBRE 


145 


Wood . . ! 177-247  cu.  ft. 

Coal 550-770  Ibs. 

Sodium  sulphate 320-395  Ibs. 

Lime 530-660  Ibs. 

The  washing,  screening  and  bleaching  of  sulphate  pulp  differ 
in  no  essential  detail  from  the  treatment  accorded  soda  pulp.  It 
is  most  general  to  use  diffusers  to  wash  the  black  liquor  from  sul- 
phate pulp  but  there  is  no  reason  why  open  pans  could  not  be 
used  and  there  is  considerable  difference  of  opinion  as  to  the  rela- 
tive advantages  of  the  two  methods.  It  is  claimed  that  the  size 
of  the  plant  influences  the  choice,  diffusers  being  satisfactory  for 
small  installations  and  open  pans  for  large  ones.  As  it  is  desirable 
to  have  five  or  six  diffusers  to  each  digester  the  cost  of  installation 
is  high  in  plants  of  large  capacity.  Moreover  their  life  is  com- 
paratively short,  —  about  ten  years,  —  due  to  the  pitting  and  eat- 
ing away  of  the  steel. 

The  yield  of  fibre  by  the  sulphate  process,  as  already  stated, 
is  greater  than  by  the  soda  process.  According  to  Kirchner 1  the 
yields  for  spruce  (Fichte)  and  fir  (Kiefer)  are: 


Soda 

Sulphate 

Sulphite 

Spruce 

Per  cent 

2Q    7—32    8 

Per  cent 
?  2  8-^t;  Q 

Per  cent 

37—^o 

Fir 

28    O—  2Q    3 

2Q    2,—  32    O 

Experiments  by  the  author  gave  the  following  yields  per  cord, 
assuming  that  there  are  100  cu.  ft.  of  solid  wood  per  cord: 


Soda 

Sulphate 

Poplar  (Populus  sp         )      

Pounds 
1007 

Pounds 
1  1  30 

White  pine  (Pinus  strobus) 

600 

772 

Pitch  pine  (Pinus  rigida)  

7QO 

862 

Spruce  (Picea  sp        ) 

786 

nc;6 

1  Kirchner:  Das  Papier,  IV,  358. 


146 


THE   SULPHATE  PROCESS 


In  addition  to  the  greater  yield  the  sulphate  fibre  bleaches 
considerably  easier  than  soda  fibre  from  the  same  wood. 

he  blow-off  gases  from  sulphate  cooks  have  been  the  subject 
of  much  investigation  in  Sweden  and  Germany.  Bergstrom  and 
Fagerlind  1  have  found  in  them  methyl  mercaptan,  dimethyl 
sulphide,  dimethyl  disulphide,  methyl  alcohol,  ammonia,  turpen- 
tine, rosin  oil,  hydrogen  sulphide,  ammonium  sulphide,  and 
acetone.  The  evil  odors  of  the  process  are  due  in  large  part  to  the 
first  two  compounds  of  which  the  mercaptan  is  far  the  worse. 
According  to  Klason  and  Segerfeld  2  about  100  grams  of  mer- 
captan are  produced  per  ton  of  wood  treated  in  making  easy 
bleaching  pulp  while  ten  times  as  much  may  be  obtained  in  kraft 
cooks.  Pine  yields  about  twice  as  much  as  spruce.  According 
to  Falk 3  the  condensed  materials  obtained  per  ton  of  cellulose 
from  pine  wood  are  as  follows:  , 


» 

In  oily  portion 

In  aqueous 
portion 

Mercaptan  

Kgs. 
o  062 

Kgs. 
o  06 

Dimethyl  sulphide  

O  .Q27 

O    17 

Dimethyl  disulphide  

o  .  103 

O    OS 

Turpentine  

8.487 

O  .02 

Distillation  residues 

O    721 

Methyl  alcohol 

r    QO 

Ammonia  

o  18 

From  work  done  at  the  Billingsfors  mill  the  condensed  steam 
from  the  digesters  was  found  to  yield  the  following  quantities 
for  every  ton  of  finished  pulp  made. 

Lbs. 

Turpentine 17.6  (from  fir) 

Turpentine 2.2  (from  pine) 

Methyl  alcohol n.o 

Methyl  mercaptan 2.  2 

Methyl  sulphide 6. 6 

Methyl  bisulphide 0.2 

Ammonia o.  4 

1  Papier-Fabr.,  1909,  7,  7,  27,  78,  104,  129. 

2  Papier-Fabr.,  1911,  9,  1093-1099. 

3  Papier-Fabr.,  1909,  7,  469-472. 


BLACK  LIQUOR  147 

^6  ergs tr 6m  l  states  that  in  1912  five  sulphate  mills  were  recover- 
ing methyl  alcohol.  Pine  and  spruce  yield  about  the  same 
amount,  15  kgs.  per  1,000  kgs.  of  cellulose,  and  of  this  5  kgs.  are 
collected  in  the  condensed  vapors  while  further  amounts  may  be 
obtained  from  the  vapors  formed  during  evaporation  of  the  black 
liquors.  The  cost  of  such  recovery  is  slight  and  the  process  in  no 
way  interferes  with  regular  operations  of  the  mill. 

Klason  2  has  carried  out  extended  investigations  of  the  sulphate 
process  in  the  attempt  to  eliminate  the  odors.  He  found  that  the 
gases  could  be  almost  entirely  freed  from  mercaptan  by  passing 
through  solutions  of  various  metallic  salts  but  that  the'  only 
metallic  mercaptides  which  were  completely  odorless  were  those 
of  the  noble  metals.  Caustic  soda  will  also  absorb  mercaptan 
but  not  methyl  sulphide.  The  gases,  separated  from  entrained 
liquid,  can  be  rendered  harmless  by  passing  them  under  a  furnace 
grate  but  explosions  must  be  guarded  against.  Oxidizing  agents, 
as  bleach  or  permanganate,  will  destroy  the  odors  but  they  also 
oxidize  the  alcohol  and  the  quantity  necessary  is  therefore  exces- 
sive. J 

THe  black  liquor  from  the  sulphate  process  has  been  inves- 
tigated repeatedly.  According  to  Klason  and  Segerfeld  3  of  the 
organic  matter  present  54.3  per  cent  is  lignin;  2.5  per  cent  fatty 
and  resin  acids;  3.7  per  cent  formic  acid;  5.2  per  cent  acetic  acid 
and  30.3  per  cent  lactonic  acids.  Of  the  sulphur  •  originally 
present  as  alkali  sulphide  51.8  per  cent  was  combined  with 
lignin,  15  per  cent  expelled  as  volatile  compounds,  16.8  per 
cent  remained  as  alkali  sulphide  and  16.4  per  cent  was  unac- 
counted for. 

The  committee  appointed  by  the  Finnish  Government 4  in 
1908  gives  the  following  composition  for  a  black  liquor  with  a 
specific  gravity  of  1.140  from  a  Swedish  mill. 

1  Papier-Fabr.,  1912,  10,  677. 

2  Papier  Ztg.,  1908,  33,  3577. 

3  Papier-Fabr.,  1911,  9,  1093-1099. 

4  Papier  Ztg.,  1910,  35,  2744. 


148  THE   SULPHATE  PROCESS 

Per  cent 

Sodium  carbonate  (Na2CO3) 2.  75 

Sodium  hydroxide  (NaOH) o.  45 

Sodium  sulphide  (Na2S) 1.76 

Sodium  sulphate  (Na2SO4) 1.21 

Sodium  sulphite  (Na2SO3) o.  16 

Sodium  chloride  (NaCl) 0. 17 

Sodium  thiosulphate  (Na2S2O3) . o.  14 

Soda  combined  with  organic  acids 2.  25 

Organic  acids 11.71 

Water,  etc 79. 40 


An  interesting  proposal  for  handling  the  black  liquor  is  that 
of  Rinman.1  He  concentrates  the  liquor  to  about  90  grams  per 
liter  of  Na20,  adds  salt  (NaCl)  to  a  strength  of  about  40  grams 
per  liter  and  precipitates  the  humus  matters  with  carbon  dioxide 
at  a  temperature  of  75°  C.  The  humus  matters  may  be  washed 
with  water,  provided  no  sodium  sulphide  is  present,  and  may 
then  be  subjected  to  destructive  distillation.  The  solution,  freed 
from  humus,  may  be  treated  by  the  ammonia-soda  process  for 
the  recovery  of  the  alkali  as  bicarbonate.  The  original  plan,  to 
recausticize  and  use  it  over  again  several  times  before  sending  it 
to  the  reclaiming  system,  has  not  proved  practical  because  of 
the  accumulation  of  substances  not  precipitated  by  carbon 
dioxide. 

As  an  alternative  to  this  process  Rinman  suggested  mixing  the 
black  liquor,  after  evaporation,  with  lime  or  caustic  soda  and 
distilling  destructively  in  presence  of  steam  at  a  temperature  of 
400°  C.  This  would  result  in  the  formation  of  fuel  gases,  acetone, 
alcohol,  ketones,  hydrocarbons,  cresols,  etc.,  and  the  residual 
carbon  would  contain  the  alkali  which  could  be  leached  out  and 
recovered.  An  experimental  plant  at  the  Stora  Kopparsberg  mill 
gave  the  following  yields  per  ton  of  pulp  made  from  pine  or  fir: 

Lbs. 

Pure  acetone 39.  6 

Motor  spirit 59-4 

Motor  oil 121.  o 

1  Rinman:  Papier-Fabr.,  1912,  10,  39  and  101. 


SODA  RECOVERY  149 

These  proposed  methods  are  rather  complicated  and  have  not 
been  generally  adopted,  much  the  greater  proportion  of  the 
alkali  being  recovered  by  the  usual  methods.  These  consist  of 
evaporation  by  any  of  the  well  known  multiple  effect  evaporators, 
by  disc  evaporators  or  combinations  of  the  two.  When  both  are 
used  the  multiple  effect  takes  the  weak  liquor  and  brings  it  up  to 
about  20°  Be.,  then  it  passes  to  the  disc  evaporator  which  concen- 
trates it  to  about  35°  Be.  According  to  Beveridge  :  in  a  well 
equipped  mill  the  water  which  the  recovery  process  must  handle 
per  2000  Ibs.  of  pulp  is  derived  from  the  following  sources: 


Cubic  feet 

Per  cent 

Water  from  chips      .  .                 .... 

47-6 

2<  .1 

Water  from  steam  

42  .48 

22  .5 

Water  from  white  liquor  
Water  used  for  washing  

67-33 
31-50 

35-6 
16.6 

188.91 

After  concentration  to  about  35°  Be.  the  liquor,  which  contains 
approximately  equal  weights  of  water  and  total  solids,  goes  to  the 
rotary  furnaces.  These  are  similar  to  the  furnaces  used  in  soda 
mills  but  are  sometimes  as  long  as  30  to  35  ft.  As  the  liquor 
works  forward  in  the  furnace  it  becomes  more  concentrated  and 
finally  burns  to  a  moist,  black  mass  still  containing  a  considerable 
amount  of  organic  matter  and  water.  In  this  form  it  is  dis- 
charged in  close  proximity  to  the  smelting  furnace  into  which  it  is 
to  be  fed.  During  the  passage  of  the  liquor  through  the  furnace 
rings  are  sometimes  formed  which  hold  it  back  while  allowing  the 
soda  near  the  discharge  end  to  become  melted  by  the  heat  from 
the  smelting  furnace.  When  the  ring  finally  breaks  and  the 
liquor  runs  into  the  melted  mass  explosions  are  very  apt  to  occur. 

After  being  discharged  from  the  rotary  furnace  the  mass  is 
mixed  with  enough  sodium  sulphate  to  replace  the  alkali  lost  and 
is  then  shoveled  by  hand  into  the  smelting  furnace.  This  is  a 
chamber  about  four  feet  square  by  seven  feet  high,  lined  with 
soapstone  to  which  the  molten  alkali  does  not  adhere,  and  so 

1  Beveridge:  Paper,  1918,  22,  349. 


THE   SULPHATE   PROCESS 


constructed  that  oxidation  of  the  sodium  sulphide  is  reduced  to  a 
minimum.  Combustion  in  the  smelting  chamber  is  provided 
for  by  an  air  blast  entering  through  tubes  which  are  water-cooled 
or  sometimes  made  of  platinum.  The  condition  of  the  entering 
ash  and  the  blast  must  be  most  carefully  regulated  to  insure 
proper  results.  Moreover  the  furnace  must  be  watched  closely  to 
see  that  the  blast  nozzles  do  not  burn  off,  due  to  a  temporary 
stoppage  of  the  water,  or  that  the  furnace  does  not  become 
clogged  and  allow  a  considerable  quantity  of  the  melt  to  collect. 
Either  of  these  conditions  is  likely  to  result  in  severe  explosions. 
The  reaction  which  takes  place  in  the  smelter  is 

Na2S04  +  4C  =  Na2S  +  4CO. 

This  is  to  a  certain  extent  reversible  as  the  oxygen  supplied  in 
the  air  blast  oxidizes  a  small  amount  of  the  sulphide  back  to 
sulphate.  For  this  reason  it  is  not  possible  to  produce  a  liquor 
entirely  free  from  sulphate,  the  proportion  depending  on  con- 
ditions in  the  smelter.  The  melt,  if  rich  in  sulphide,  is  of  a  red- 
dish color.  The  composition  of  various  samples  is  as  follows : 1 


Authority 

Kgs.  sul- 
phate per 
100  kgs. 
melt 

Composition  of  melt  in  per  cents 

Na2CO3 

NaOH 

Na2S 

Na2SO3 

Na2S04 

Insol- 
uble 

M  Muller 

23-7 
II  .0 
8-10 
8-10 

20-22 
20-22 
2O-22 

56.60 
71.40 
80.26 
74.20 
59-42 
62  .07 

68.37 
61.73 

0.40 
0.50 
1.04 
1.  60 

O.2O 
2  .20 

3-50 

22.60 
II  .60 
7-15 
9-50 
14.00 

17-75 
13-75 
21.50 

2.80 
1.40 

7-33 

12.70 
9.80 
5-36 
6.58 

I3-3I 
8.04 
11.40 

2.78 

1.89 
3.65 
8.14 
5-10 
i.  60 
1.90 

W.  Schacht                .    .  . 

n 

« 

it 

Klason  and  Segerfelt*.  . 

*  Papier-Fabr.,  1911,  9, 1093-1099. 


Beveridge 2  gives  the  relationship  between  the  melt,  its  solu- 
tion, and  the  causticized  liquor  as  follows: 


1  Kirchner:  Das  Papier,  105,  279. 

2  Beveridge:  Paper,  1918,  22,  21. 


REDUCING  ODORS 


Melt,  per  cent 

Solution  of 
melt,  grams 
per  liter 

Causticized 
liquor,  grams 
per  liter 

Na2CO3 

62  44 

212   85 

13  8 

Na2S                                   

26  .06 

104   17 

28   7 

Na2SO4                  

4.26 

1^.84 

7  Q2 

NaOH                   

8l.l 

SiO2          

2  .35 

Insol.  in  water  

6.18 

From  the  smelting  furnace  the  melt  flows  in  a  red  hot  con- 
dition to  dissolving  tanks  containing  water  or  the  dilute  washings 
from  the  lime  sludge  in  the  causticizing  room.  When  the  solu- 
tion has  reached  the  desired  density  it  is  discharged  into  the 
causticizing  system.  This  solution  generally  has  a  greenish  tint 
from  which  it  is  termed  "  green  liquor  "  to  distinguish  it  from  the 
"  white  liquor "  obtained  after  causticizing.  The  dissolving 
tanks  must  be  cleaned  out  occasionally  because  a  certain  amount 
of  mud  collects  in  them;  this  mud  should  be  used  in  the  caus- 
ticizing system  in  order  to  utilize  the  soda  which  it  contains. 

The  gases  from  the  recovery  furnaces  have  been  analysed  by 
Klason1  and  found  to  contain  13  mgs.  of  methyl  mercaptan  and 
4  mgs.  of  hydrogen  sulphide  per  cubic  meter.  Careful  blowing 
off  from  the  digester  reduces  this  by  about  one-third  by  removing 
more  from  the  black  liquor.  The  gases  from  the  calciners  can- 
not be  washed  commercially  on  account  of  the  great  size  of  the 
scrubbers  required  and  the  slight  solubility  of  the  impurities  in 
water.  On  account  of  their  great  dilution  only  a  small  part 
could  be  burned  by  passing  under  the  grates  of  the  boilers.  In 
order  to  reduce  the  formation  of  bad  odors  to  a  minimum  the 
digesters  should  be  blown  off  until  the  condensed  distillate  has 
no  odor,  the  black  liquor  should  be  evaporated  to  such  a  point  that 
it  will  not  cool  the  fires  enough  to  cause  distillation  or  incomplete 
combustion,  and  the  calciner  should  be  given  plenty  of  air.  Lead 
acetate  paper  may  be  used  as  a  test  in  controlling  the  running  of 
the  calciner.-. 

Klason:  Papier  Ztg.,  1908,  33,  3619. 


152  THE   SULPHATE   PROCESS 

The  methods  for  the  analysis  of  the  liquors  and  the  recovered 
ash  in  the  sulphate  process  are  more  complicated  than  for  similar 
products  in  the  soda  process.  The  following  procedure  for  white 
liquor  has  been  worked  out  in  the  Forest  Products  Laboratory 1 
and  found  to  be  accurate  except  in  the  presence  of  polysulphide. 

(a)  Total  Alkali. 

Two  c.c.  of  the  liquor  are  titrated  with  half  normal  acid  using 
methyl  orange  as  an  indicator.  This  gives  the  acid  equivalent 
to  the  Na2CO3,  NaOH,  Na2S  and  \  Na2SO3. 

(b)  NaOH  and  Na2S. 

To  2  c.c.  of  the  solution  contained  in  a  100  c.c.  flask  add  20  c.c. 
of  a  10  per  cent  solution  of  BaCl2  and  make  up  to  the  mark  with 
boiling  distilled  water;  shake  for  a  few  minutes  and  allow  to 
settle;  cool  and  draw  off  50  c.c.  of  the  clear  liquid  and  titrate 
with  half  normal  acid,  using  methyl  orange  as  indicator. 

(c)  Sodium  sulphide  +  Na2S203  +  Na2SOs. 

Find  by  trial  the  approximate  amount  of  standard  iodine 
necessary  to  react  with  2  c.c.  of  the  liquor.  Using  about  half  a 
c.c.  less  than  this  amount  of  iodine  in  200  c.c.  of  water  add  2  c.c. 
of  the  liquor,  acidify  with  acetic  acid  and  complete  the  titration 
with  iodine  using  starch  as  an  indicator.  This  shows  the  iodine 
equivalent  to  the  Na2S,  Na2S2O3  and  Na2SOs. 

(d)  Na2S203  +  Na2S03. 

To  5  c.c.  of  the  solution  in  a  250  c.c.  graduated  flask  add  an 
excess  of  an  alkaline  solution  of  zinc  chloride;  make  up  to  the 
mark,  shake  for  a  few  minutes,  and  allow  to  settle;  draw  off 
50  c.c.  of  the  clear  solution,  and  neutralize  with  sulphuric  acid 
using  methyl  orange  as  an  indicator.  Titrate  this  solution  with 
tenth  normal  iodine  using  starch  as  indicator;  decolorize  by  add- 
ing one  drop  of  sodium  thiosulphate  solution  and  titrate  to  neu- 
trality with  tenth  normal  sodium  hydroxide.  The  number  of  c.c. 

1  Paper,  Feb.  23,  1916,  p.  30. 


METHODS   OF   ANALYSIS  153 

multiplied  by  0.0042  gives  the  amount  of  Na2SOs  in  the  sample 
and  this  figure  divided  by  0.0063  gives  the  iodine  value  of  the 
sodium  sulphite.  Subtract  this  from  the  iodine  titration  previ- 
ously obtained,  which  will  give  the  iodine  equivalent  to  the  so- 
dium thiosulphate  present. 

Calculations. 

c  —  d  gives  the  c.c.  of  iodine  for  sodium  sulphide. 

a  —  b  gives  the  c.c.  for  Na2C03  and  \  Na2SO3. 

The  titration  in  (b)  expressed  as  Na2O,  minus  the  sodium 

sulphide  as  Na2O,  gives  the  Na2O  equivalent  to  the  NaOH 

present. 

This  same  procedure  may  be  employed  for  the  examination  of 
the  recovered  ash  in  which  case  50  grams  of  the  sample  are  dis- 
solved in  about  400  c.c.  of  freshly  distilled  water  and  after  shaking 
repeatedly  for  two  hours  made  up  to  500  c.c. 

This  does  not  include  the  determination  of  Na2S04  which  may 
be  accomplished  by  acidulating  a  measured  volume  of  the  solu- 
tion with  HC1,  boiling  till  all  H2S  is  driven  off  and  then  pre- 
cipitating the  sulphate  with  BaCl2.  The  BaSCX  is  filtered  off, 
washed,  ignited  and  weighed  and  from  this  weight  that  of  the 
Na2S04  may  be  calculated. 

For  a  quick  method  of  analysis  for  the  control  of  the  cooking 
liquor  Heuser  l  recommends  the  following: 

Dilute  10  c.c.  of  the  liquor  to  100  c.c. 

N  . 

(1)  Treat  10  c.c.  of  the  dilute  liquor  with  an  excess  of  —  iodine 

10 

N 

solution  and  determine  the  excess  with  —  thiosulphate  using 

10 

starch  as  an  indicator.     Calculate  to  Na2S. 

(2)  Heat  10  c.c.  of  the  dilute  liquor  with  an  excess  of  —  Ha2SO4 

10 

till  the  odor  of  H2S  is  gone  and  then  titrate  back  with  —  Ba(OH)2 

10 

using  phenolphthalein  as  indicator.  This  gives  Na2S,  NaOH  and 
Na2CO3. 

1  Private  communication. 


154  THE   SULPHATE   PROCESS 

(3)  Treat  10  c.c.  of  the  dilute  liquor  with  10  per  cent  BaCl2 

solution  and  titrate  with  —  H2S04.     This  gives  NaOH  and  Na2S. 

10 

Calculations. 

(3)  -  (i)  =  NaOH. 
(2)  -  (3)  =  Na2C03. 
(i)  =  Na2S. 

Moe l  uses  a  silver  nitrate  solution  containing  87.89  gms. 
AgN03  per  liter  for  determining  sulphides.  When  i  c.c.  is 
titrated  the  c.c.  of  AgNO3  used  represent  pounds  of  Na2S  per 
cubic  foot  of  liquor.  He  gets  the  end  point  directly  in  the  solu- 
tion by  shaking  to  coagulate  the  silver  sulphide,  and  noting  the 
point  at  which  no  further  precipitate  is  formed  by  a  drop  of  the 
silver  nitrate. 

Oliver 2  works  in  a  somewhat  similar  way  but  uses  an  ammoni- 
acal  silver  nitrate  solution.  The  liquor  to  be  tested  is  filtered, 
made  ammoniacal  and  boiled.  The  end  point  is  determined  by 
filtering,  adding  more  silver  nitrate  and  repeating  till  a  drop 
causes  only  a  slight  opacity. 

The  examination  of  black  liquor  for  total  alkali  may  be  per- 
formed exactly  as  in  the  case  of  liquor  from  the  soda  process.  The 
method  for  caustic  soda,  given  under  the  soda  process,  if  applied 
to  sulphate  black  liquor  will  show  both  the  caustic  soda  and  the 
sodium  sulphide  present  so  that  a  correction  for  the  latter  is 
necessary. 

For  the  determination  of  sodium  sulphide  in  black  liquor  the 
Forest  Products  Laboratory  recommends  the  following  method: 

Prepare  a  standard  zinc  solution  by  dissolving  16.746  grams  of 
pure  zinc  in  a  small  excess  of  nitric  acid  and  adding  ammonia 
till  the  precipitate  formed  is  completely  redissolved.  The  solu- 
tion is  diluted  to  2000  c.c.  and  enough  ammonia  must  be  present 
to  keep  the  zinc  from  precipitating  at  this  dilution. 

As  indicator  use  a  solution  of  nickel  ammonium  sulphate  made 
alkaline  with  ammonia. 

1  Paper,  Aug.  12,  1914,  p.  19.  2  Paper,  July  22,  1914,  p.  20. 


METHODS   OF  ANALYSIS  155 

For  the  determination  50  c.c.  of  black  liquor  are  diluted  to 
1000  c.c.  and  20  c.c.  taken  for  the  test.  This  is  diluted  to  about 
100  c.c.  and  the  zinc  solution  run  in  from  a  burette.  The  end 
point  is  determined  by  noting  whether  a  precipitate  of  black  NiS 
is  formed  when  a  little  of  the  solution  being  titrated  is  added  to 
three  drops  of  the  ammoniacal  NiSCX  solution  on  a  spot  plate. 

Each  c.c.  of  the  zinc  solution  equals  o.oio  grams 


CHAPTER  VI 
THE   SULPHITE   PROCESS 

The  first  patent  relating  to  the  use  of  sulphurous  acid  in  pre- 
paring pulp  from  wood  was  that  granted  to  B.  C.  Tilghman  in 
I867.1  This  was  followed  in  1869  by  a  supplementary  patent 
covering  the  treatment  of  fibrous  materials  at  ordinary  pressures, 
and  it  is  upon  these  two  patents  that  subsequent  modifications 
of  the  process  are  based.  The  specifications  of  the  original 
patent  show  that  Tilghman  had  worked  out  his  process  in  an 
experimental  way  with  great  care  and  thoroughness  and  that  he 
fully  understood  all  its  possibilities.  In  its  practical  application, 
however,  difficulties  of  an  engineering  nature  arose  which  proved 
too  serious  for  him  to  overcome. 

After  his  failure  the  process  was  taken  up  by  Ekman  and  Fry  in 
Sweden,  by  Mitscherlich  in  Germany,  by  Francke,  Graham, 
Ritter,  Kellner  and  numerous  other  investigators  and  manu- 
facturers and  the  engineering  difficulties  were  gradually  over- 
come so  that  finally  the  process  was  established  on  a  firm  footing. 

Theory  of  the  Sulphite  Process.  Probably  the  best  explana- 
tion of  the  sulphite  cooking  process  is  that  it  is  primarily  a  hydro- 
lytic  splitting  of  the  cellulose-lignin  esters  followed  by  secondary 
decompositions  of  the  lignin.  Water  alone  at  high  temperatures 
will  hydrolyze  lignocellulose  rendering  part  soluble,  but  in  the 
presence  of  an  acid,  such  as  sulphurous  acid,  the  reaction  pro- 
ceeds much  more  rapidly  and  at  a  lower  temperature.  For- 
tunately cellulose  itself  is  comparatively  stable  under  such  condi- 
tions but  that  it  is  by  no  means  unattacked  has  been  shown  by 
Tauss  and  others.  When  a  substance  is  present  which  will  com- 
bine with  the  products  of  hydrolysis  and  remove  them  from  the 

1  U.  S.  Pat.  70,483,  Nov.  5,  1867. 
156 


WOOD   AND    ITS   PREPARATION  157 

sphere  of  action  the  reaction  will  proceed  to  the  limit  fixed  by  the 
constitution  of  the  lignocellulose.  Such  substances  are  the 
sulphites  which  during  the  reaction  form  true  chemical  com- 
pounds with  the  aldehydic  products  of  decomposition.  The 
organic  acids  formed  during  the  decomposition  of  the  lignin  also 
combine  with  the  sulphites  and  thereby  set  free  an  equivalent 
amount  of  sulphurous  acid.  During  the  latter  part  of  a  cook 
this  causes  a  steady  increase  in  the  amount  of  gas  which  necessi- 
tates "  blowing  off  "  to  prevent  too  great  pressure. 

According  to  Klason  l  lignin  is  a  glucoside-like  body  of  which 
a  part  is  sugar-like  or  cellulose  while  the  other  part  is  of  an 
aromatic  nature.     This  contains  an  oxypropylene  group, 
-CH=  CH  -CH2OH, 

as  well  as  methoxyl,  hydroxyl  and  aldehyde  groups.  It  is  closely 
related  to  coniferyl  alcohol.  In  the  sulphite  process  sulphurous 
acid  is  taken  into  the  double  bond 

=  C  =  C 

II  +  H2SO3  =        I 
=  C  =  CSO2OH 

and  forms  the  calcium  salt  of  lignin  sulphonic  acid, 

C18H1908SCai. 

Secondary  reactions  may  cause  the  formation  of  calcium  sul- 
phate, either  from  the  decomposition  of  the  calcium  bisulphite 
according  to  the  reaction : 

3  Ca  (HS03)2  =  3  CaS04  +  H2S04  +  S2  +  2  H20 

or  from  reduction  of  tannin  with  consequent  oxidation  of  sul- 
phurous acid.  This  latter  reaction  explains  the  difficulty  in 
using  wood  rich  in  tannin. 

Wood  and  Its  Preparation.  One  of  the  chief  requisites  for 
wood  to  be  used  in  the  sulphite  process  is  freedom  from  any 
excessive  amount  of  rosin,  and  of  nearly  equal  importance  is  the 
even  distribution  of  that  which  is  present.  If  the  rosin  is  local- 
ized at  certain  points  the  wood  at  those  places  will  remain  hard 

1  A.  Klein:  Papier  Ztg.,  1906,  p.  474. 


158  THE  SULPHITE  PROCESS 

and  will  cause  shives  in  the  pulp  from  the  portions  which  are 
easily  reduced. 

In  the  sulphite  process  the  liquor  has  not  nearly  the  solvent 
power  of  the  alkali  used  in  the  soda  process  and  any  bark,  decayed 
portions  or  knots  which  go  into  the  digester  are  likely  to  appear 
as  dirt  in  the  finished  pulp.  This  applies  to  the  light-colored 
inner  bark  if  the  product  is  to  be  used  unbleached,  since  it  takes 
on  a  dark  color  and  shows  in  the  pulp  as  dark  fibres.  For 
bleached  -  pulp,  however,  this  inner  bark  is  harmless,  since  it 
bleaches  quite  as  readily  as  the  rest. 

The  removal  of  the  bark  is  accomplished  practically  in  a  num- 
ber of  ways.  Hand  peeling  in  the  woods  is  not  so  usual  for 
spruce  though  it  is  quite  general  for  the  poplar  used  in  the  soda 
process.  Disc  barkers  of  various  types  are  most  commonly 
used;  in  these  the  log  is  held  by  hand  or  machinery  against 
knives  fastened  to  a  rapidly  revolving  disc.  These  knives  remove 
much  wood  as  well  as  bark,  particularly  where  the  sticks  are 
crooked.  The  amount  of  such  loss  depends  on  the  size  of  the 
logs  as  well  as  the  care  with  which  the  work  is  done;  the  sound 
wood  lost  may  amount  to  8  to  20  per  cent  of  the  original  weight 
of  the  logs,  in  addition  to  the  8  to  10  per  cent  of  true  bark;  the 
total  loss,  therefore,  amounts  to  16  to  30  per  cent  of  the  logs  as 
received.  The  drum  barker,  which  is  a  device  to  remove  the  bark 
by  rubbing  the  logs  against  one  another  and  the  sides  of  the  drum, 
saves  all  this  loss  of  wood.  It  is,  however,  expensive  to  install, 
requires  more  power  than  other  barkers  to  do  the  same  amount 
of  work,  and  in  winter  the  water  used  in  it  has  to  be  heated,  which 
adds  to  the  expense.  This  type  of  barker  is  suitable  only  where 
very  clean  pulp  is  not  essential  or  where  bleached  pulp  is  to  be 
made  as  it  does  not  remove  all  the  thin  inner  bark.  It  is  best 
applied  to  wood  which  has  been  in  the  water  two  or  three  months 
as  the  bark  is  then  more  readily  removed.  Of  the  drum  barkers 
the  intermittent  give  better  results  than  the  continuous. 

With  any  system  of  barking  the  logs  should  be  inspected  on 
the  conveyor  as  they  go  to  the  chipper,  and  any  with  bark  remain- 
ing in  cracks  or  around  knots  put  at  one  side  to  be  cleaned  by 


WOOD   AND  ITS   PREPARATION  159 

hand.  Some  operators  clean  very  little  by  hand  but  put  the 
defective  wood  at  one  side  to  be  cooked  separately  into  second 
grade  stock.  This  necessitates  a  very  thorough  cleaning  up  of 
all  apparatus  afterwards. 

The  barked  wood  next  goes  to  the  chippers  which  should  be 
run  slowly  enough  to  produce  even  chips.     The  length  of  chip 


FIG.  21.  '  PULP  WOOD  CHIPPER 

depends  on  the  method  of  cooking  as  well  as  the  kind  of  wood. 
For  hemlock  they  should  be  J  to  J  inch  long  while  spruce  is 
chipped  about  as  follows: 

For  Mitscherlich  unbleachable  i  J  to  if  inches  long. 

For  quick  cook,  newsprint  stock  f  to  i  inch  long. 

For  easy  bleaching  f  to  f  inch  long. 

The  coarse  chips  are  generally  further  reduced  in  size  by  some 
sort  of  crusher  and  are  then  screened  to  remove  coarse  pieces, 
which  are  rechipped,  and  sawdust,  which  goes  to  waste.  The  saw- 
dust from  chipping  should  not  amount  to  more  than  3  per  cent. 

The  knots  may  be  removed  from  the  chips  in  several  ways;  one 
very  successful  process  is  to  blow  them  against  an  inclined  wire 


160  THE   SULPHITE  PROCESS 

screen  through  which  the  dust  and  fine  material  passes  while  the 
good  chips  slide  down  the  screen  and  are  collected  on  a  conveyor. 
By  proper  adjustment  of  the  air  blast  the  knots,  being  heavier 
than  the  good  chips,  fall  short  of  the  screen  and  are  collected  by 
a  separate  conveyor.  Another  method,  which  also  makes  use  of 
the  difference  in  weight  of  the  good  chips  and  knots,  is  that  of 
passing  the  dry  chips  through  a  trough  of  water.  The  good 
chips  float  and  are  removed  by  a  conveyor  which  passes  across  the 
surface  of  the  tank,  while  the  knots,  being  heavier  than  water, 
sink  to  the  bottom  and  can  be  removed  by  scrapers. 

Uniformity  and  cleanliness  of  chips  are  essential  to  clean  pulp 
and  good  yield  and  all  chips  cooked  in  the  same  charge  should  be 
of  one  kind  of  wood  and  as  nearly  as  possible  of  the  same  age  and 
moisture  content.  Much  difference  of  opinion  exists  as  to  the 
relative  desirability  of  wet  or  seasoned  wood.  Many  prefer  dry, 
well  seasoned  chips,  claiming  more  rapid  penetration  of  the 
liquor  and  better  yield;  others  1  state  that  green  wood  or  that 
which  has  lain  in  the  water  for  some  time  is  reduced  more  easily 
than  seasoned  wood.  Experiments  by  the  author  tend  to  confirm 
this  latter  opinion,  as  in  certain  cases  woods  which  could  not  be 
successfully  treated  dry  readily  yielded  to  the  acid  if  they  were 
saturated  with  water  before  cooking. 

The  capacities  of  wood  handling  machinery  vary  enormously 
under  the  conditions  of  operation  but  they  may  be  said  to  be 
approximately  as  follows. 

Circular  and  band  saws . up  to  50  cords  per  hour. 

Drum  barkers •. 1-4  cords  per  hour. 

Disc  barkers i.  2-1. 4  cords  per  hour. 

Chippers 10-15  cords  per  hour. 

Flat  screens -3*5-  cord  per  sq.  ft.  per  hour. 

Liquor  Making.  The  liquor  or  acid  used  in  the  sulphite 
process  is  an  aqueous  solution  of  sulphurous  acid  in  which  lime, 
or  some  other  base,  has  been  dissolved;  the  final  result  is  there- 
fore a  solution  of  the  bisulphite  of  the  base  containing  an  excess 
of  sulphurous  acid.  In  practice  this  is  prepared  in  two  different 
1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  189. 


PREPARATION   OF   SULPHUR  DIOXIDE  l6l 

ways:  by  passing  the  gas  through  water  in  which  the  base  is 
dissolved  or  suspended,  or  by  bringing  the  gas  into  contact  with 
comparatively  large  lumps  of  the  carbonate  of  the  base  which 
are  moistened  by  a  continuous  flow  of  water.  The  first  effect  of 
this  treatment  is  the  solution  of  the  gas  in  water  forming  the  true 
sulphurous  acid: 

H20  +  S02  =  H2S03. 

This  then  attacks  the  base  according  to  one  of  the  following 
reactions : 

Ca  (OH)2  +  H2S03  =  CaS03  +  2  H2O. 
or  CaC03  +  H2SO3  =  CaS03  +  H2O  +  CO2.      • 

If  the  base  is  soda  or  magnesia  the  sulphites  stay  in  solution  but 
if  lime  is  used  calcium  sulphite  is  precipitated  as  fast  as  it  i£ 
formed  since  it  is  very  insoluble,  one  part  requiring  about  800 
parts  of  cold  water  for  its  solution.  In  the  first  method,  working 
with  milk  of  lime,  the  formation  of  sulphite  continues  until  all  the 
lime  is  precipitated;  further  passage  of  the  gas  then  causes  this 
to  redissolve  with  formation  of  the  bisulphite.  When  limestone 
or  dolomite  is  used,  as  in  the  second  method,  its  surface  grad- 
ually crusts  over  with  the  sulphite  which  is  again  brought  into 
solution  as  more  gas  is  dissolved.  Both  of  these  reactions  doubt- 
less take  place  simultaneously  when  there  is  a  liberal  supply  of  gas. 

Of  the  available  bases  for  making  sulphite  liquor  soda  has  the 
advantage  of  forming  a  stable  bisulphite  and  the  cellulose  pre- 
pared with  such  liquor  is  very  pure  and  easy  to  bleach.  Magnesia 
possesses  these  qualities,  but  in  a  lesser  degree,  while  lime  is 
likely  to  make  the  fibre  hard  and  harsh  from  formation  of  calcium 
monosulphite. 

Preparation  of  Sulphur  Dioxide.  Sulphur  dioxide  for  use  in 
the  absorption  system  is  prepared  by  burning  either  sulphur  or 
iron  pyrites  and  with  proper  care  good  results  can  be  obtained 
by  either  method.  The  choice  of  the  two  processes  depends  to 
a  great  extent  on  local  conditions,  such  as  the  relative  cost  of  the 
two  materials,  the  possibility  of  disposing  of  the  spent  oxide 
from  the  pyrites,  the  floor  space  available,  etc.;  it  is  much  more 
of  a  financial  problem  than  a  technical  one. 


162  THE  SULPHITE  PROCESS. 

Sulphur  burning  was  formerly  carried  on  very  largely  in  the 
retort  type  of  furnaces  into  which  the  sulphur  was  fed  through  a 
door  at  one  end.  This  caused  gas  of  irregular  composition  due 
to  the  sudden  rush  of  cold  air  into  the  furnace  and  through  the 
apparatus.  This  type  of  furnace  was  suitable  for  very  pure  sul- 
phur, particularly  Sicilian,  but  when  there  was  a  tendency  for 
the  sulphur  to  form  an  oily  surface  scum  during  burning  good 
results  were  not  obtained.  This  trouble  can  be  overcome  by 


FIG.  22.    ROTARY  SULPHUR  BURNER 

installing  rakes  which  travel  slowly  back  and  forth,  breaking  up 
the  scum  and  presenting  fresh  surfaces  for  combustion.  With 
this  device  the  flat  burners  give  excellent  results. 

Modern  sulphur  burners  are  of  two  quite  dissimilar  forms  — 
one  a  horizontal  rotary  furnace  and  the  other  vertical  and  sta- 
tionary. In  the  rotary  burner,  illustrated  in  Fig.  22,  the  sulphur 
enters  from  the  hopper  at  the  front  end  and  gradually  works 
toward  the  back.  As  the  burner  revolves  the  sulphur  is  carried 
up  the  sides  and  thus  presents  a  large  and  continually  renewed 
surface  for  combustion.  A  highly  successful  modification  of  the 
sulphur  feed  is  to  introduce  it  in  the  molten  condition  through  a 
pipe  entering  at  the  axis  of  the  burner.  A  continuous  supply  of 


PREPARATION  OF  SULPHUR  DIOXIDE 


163 


molten  sulphur  may  be  obtained  by  placing  the  crude  sulphur 
in  a  steam  jacketed  tank  and  also  surrounding  the  delivery  pipe 
with  a  steam  jacket  so  that  the  sulphur  will  not  solidify  before  it 


Patented 

Serial  Number 

837046 


FIG.  23.    VESUVIUS  SULPHUR  BURNER 
Courtesy  of  Valley  Iron  Works  Company 

reaches  the  burner.  Users  of  this  type  of  burner  claim  that  it  is 
the  best  if  it  is  fitted  with  self-feeding  device  and  a  large  com- 
bustion chamber  because  it  makes  stronger  and  more  uniform 
gas  and  starts  and  stops  very  quickly  in  case  of  shutdowns. 


THE  SULPHITE  PROCESS 


C.L.Door 


FIG.  24.    VESUVIUS  SULPHUR  BURNER,  SECTIONAL  VIEW 
Courtesy  of  Valley  Iron  Works  Company 

The  stationary  type  of  burner  is  illustrated  in  Figs.  23  and  24. 
It  consists  of  a  vertical  cylinder  lined  with  fire  brick  and  fitted 
with  four  combustion  trays  or  shelves.  The  sulphur  is  introduced 
through  a  melting  chamber  at  the  top  and  flows  downward  from 


PREPARATION  OF  SULPHUR  DIOXIDE  165 

one  tray  to  the  next.  The  ash  and  residue  from  the  sulphur  col- 
lect at  the  bottom  and  if  at  any  time  they  accumulate  on  the 
shelves  they  can  be  flushed  downward  by  a  sudden  increase  in  the 
sulphur  feed.  This  burner  has  no  moving  parts  and  therefore 
requires  no  power.  The  makers  claim  that  a  burner  a  little  less 
than  7  ft.  high  over  all  and  occupying  a  floor  space  6  ft.  square 
has  a  capacity  of  9  tons  per  twenty-four  hours.  It  is  the  exper- 
ience of  numerous  operators  that  burners  of  this  type  are  difficult 
to  run  satisfactorily. 

The  most  important  factor  in  sulphur  burning  is  the  regulation 
of  the  air  supply.  One  pound  of  sulphur  requires  for  its  complete 
combustion  just  one  pound  of  oxygen,  which  is  the  amount  con- 
tained in  53.8  cu.  ft.  of  air.  If  much  more  air  is  admitted,  and 
particularly  if  it  contains  much  moisture,  there  is  a  formation  of 
S03  and  sulphuric  acid  which  causes  loss  of  both  lime  and  sul- 
phur. According  to  Frohberg  1  the  maximum  formation  of  SO3 
takes  place  at  400°  to  500°  C.  while  at  900°  to  1000°  C.  it  is  again 
broken  up  into  sulphur  dioxide  and  oxygen.  He  recommends 
running  the  furnaces  as  hot  as  possible  to  produce  rich  gas  which 
should  then  be  at  once  sprayed  with  cold  water  to  reduce  its 
temperature  to  90°  to  100°  C.  In  one  modern  American  mill  the 
best  temperature,  measured  at  the  outlet  of  the  combustion 
chamber,  is  considered  to  be  620°  C.,  while  variations  from  480° 
to  680°  C.  sometimes  occur. 

According  to  Cosier2  poor  cooling  may  be  responsible  for 
excessive  formation  of  S03,  weak  cooking  acid  and  low  free  S02. 
Acid  saturated  with  CaSCX  may  carry  into  the  digesters  as  much 
as  55  Ibs.  per  ton  of  chips.  This  is  largely  precipitated  at  the 
temperature  of  cooking  and  may  cause  poor  penetration  and 
necessitate  a  high  temperature  to  finish  the  cook.  The  elimina- 
tion of  SOs  can  be  assured  by  employing  the  Cottrell  electrical 
precipitation  process  or  filtering  the  gas  through  sawdust  as 
recommended  by  Paulson.3 

1  Chem.  Ztg.,  1914,  38,  126. 

2  Cosier:  Paper,  1918,  Feb.  13,  p.  19. 

3  Paper,  1917,  21,  Oct.  3,  p.  32. 


1 66  THE  SULPHITE  PROCESS 

Any  overheating  of  the  burner  is  likely  to  cause  vaporization 
of  unconsumed  sulphur  which  passes  along  with  the  gases  until 
it  reaches  the  colder  portions  of  the  system  where  it  condenses. 
Sublimation  of  sulphur  also  occurs  when  too  little  air  is  admitted 
after  the  burner  has  become  thoroughly  heated  up  since  there  is 
then  too  little  oxygen  present  to  combine  with  all  the  sulphur 
vapor.  The  sublimation  of  sulphur  is  likely  to  lead  to  the 
formation  of  thiosulphuric  and  polythionic  acids  which  at  the 
temperature  of  cooking  again  break  down  with  the  liberation  of 
sulphur.  Free  sulphur  may  also  appear  in  the  acid  from  direct 
contamination  with  sublimed  sulphur.  Klason  claims  that  a  liquor 
may  contain  as  much  as  250  mgs.  per  liter  of  sulphur  as  thiosul- 
phuric acid  before  sulphur  is  formed  in  the  digester  and  as  under 
normal  conditions  the  fresh  liquor  contains  only  about  3  mgs.  per 
liter  of  sulphur  the  danger  from  this  source  is  not  very  great. 

The  conditions  under  which  a  burner  is  working  may  be  judged 
from  the  appearance  of  the  flame.  When  operating  satisfac- 
torily it  is  blue,  sometimes  tipped  with  white;  if  it  shows  brown 
fumes  of  unconsumed  sulphur  vapor  it  indicates  that  the  furnace 
is  too  hot,  probably  from  the  use  of  too  much  air,  and  that  there 
is  danger  of  sublimation. 

Attached  to,  or  immediately  adjoining,  nearly  every  type  of 
sulphur  burner  is  a  combustion  chamber  which  the  gas  enters  as 
soon  as  it  leaves  the  burner  proper.  This  is  so  arranged  that  more 
or  less  air  can  be  admitted  at  will  through  appropriate  dampers 
and  in  this  way  sublimed  sulphur  carried  along  from  the  burner 
can  be  completely  burned  to  sulphur  dioxide. 

The  burning  of  pyrites  in  the  old  type  of  burners  was  con- 
siderably more  difficult  to  control  than  the  burning  of  sulphur 
and  it  could  be  worked  advantageously  only  where  the  burners 
could  be  grouped  together  in  sufficient  numbers  to  insure  gas  of 
even  composition.  Many  of  these  difficulties  have  been  over- 
come by  modern  mechanical  furnaces  of  which  the  Herreshoff  fur- 
nace is  a  type.  These  burners  (see  Fig.  25)  usually  have  five 
shelves  over  which  the  pyrites  is  raked  in  succession  by  mechan- 
ically operated  rakes.  The  shafts  and  arms  are  hollow  and  are 


PREPARATION  OF   SULPHUR   DIOXIDE 


I67 


cooled  by  a  current  of  air  supplied  by  a  fan;  part  of  the  hot  air 
thus  produced  is  used  in  the  lower  parts  of  the  chamber  and 
materially  assists  combustion.  The  heat  produced  by  the  oxida- 
tion of  the  sulphur  and  iron  is.  sufficient  for  carrying  on  the  opera- 
tion and  once  the  furnace  is  in  good  working  condition  no  fuel  is 
required.  The  spent  pyrites  or  cinders  leaves  the  furnace  with 
\  per  cent  to  4  per  cent  of  sulphur.  The  separation  of  dust  is 


FIG.  25.    HERRESHOFF  PYRITES  BURNER 

particularly  important  where  pyrites  is  used.  This  was  formerly 
done  by  passing  the  gas  through  long  chambers  of  large  area  so 
that  the  velocity  of  the  gas  should  be  slight.  In  modern  practice 
it  is  more  successfully  accomplished  by  passing  the  gas  through 
towers  into  which  water  is  sprayed;  this  not  only  removes  dust 


1 68 


THE  SULPHITE  PROCESS 


but  also  takes  out  S03  and  cools  the  gas.  Provided  the  wash 
water  is  discharged  at  175°  F.  (80°  C.)  the  loss  from  dissolved 
S02  is  very  slight. 

The  gas  from  sulphur  burners  operating  under  satisfactory 
conditions  generally  contains  14  to  1 8  per  cent  of  S02  by  volume; 
the  maximum  which  it  can  possibly  contain  is  21  per  cent.  In 
the  case  of  pyrites  the  theoretical  maximum  is  16.2  per  cent  of 
SOz  and  it  generally  runs  about  10  to  14  per  cent.  As  a  rule  when 
burning  sulphur  about  2  to  3  per  cent  is  converted  into  S03  while 
with  pyrites  as  much  as  13  per  cent  may  be  lost  in  that  way. 

After  leaving  the  combustion  chambers  the  gas  is  conveyed 
through  iron  pipes  to  the  coolers.  Up  to  this  point  the  gas  is  hot 
and  dry  and  has  little  action  on  iron  but  for  the  cooler  and  all 
pipes  beyond  lead  should  be  used.  The  cooler  generally  con- 
sists of  lead  pipes  through  which  the  gas  passes  back  and  forth. 
These  pipes  are  placed  in  a  trough  through  which  water  flows,  or 
are  so  arranged  that  a  thin  film  of  water  trickles  over  them.  The 
cooling  surface  should  be  about  15  sq.  ft.  per  ton  of  daily  produc- 
tion which  is  sufficient  to  bring  the  gas  nearly  to  the  temperature 
of  the  water  in  summer.  In  winter  the  gas  should  be  cooled  to 
about  55°  F.  (12.8°  C.).  Regular  and  uniform  cooling  of  the  gas 
is  very  important  as  the  rate  of  absorption  and  the  quantity  of 
gas  dissolved  depend  very  largely  upon  the  temperature.  The 
following  table  l  shows  how  rapidly  the  quantity  of  gas  absorbed 
decreases  with  rise  in  temperature. 


Temperature 

i  vol.  of  water  dis- 
solves SO2 

i  vol.  of  solution 
contains  SO2 

Degs.  C. 

Vols. 

Vols. 

o 

79-79 

68.86 

10 

56.65 

5I-38 

20 

39-37 

36.21 

30 

27  .16 

25.82 

40 

18.77 

17  .01 

Absorption  Apparatus.    The  apparatus  in  which  the  bisul- 
phite solution  is  prepared  depends  on  whether  the  base  is  used 

1  Schonfeld:  Ann.,  95,  5. 


ABSORPTION  APPARATUS 


in  suspension  or  in  lumps  of  con- 
siderable size.  In  the  first  class 
come  the  apparatus  of  Partington, 
McDougall,  Frank,  Burgess,  Steb- 
bins,  Barker,  etc.,  while  in  the 
second  class  are  the  systems  of 
Flodquist,  Mitscherlich,  Kellner, 
Ekman,  Jenssen,  etc.  As  the 
tower  is  the  oldest  and  in  some 
ways  the  simplest  form  of  absorp- 
tion apparatus  it  will  be  con- 
sidered first. 

The  essential  feature  of  the 
Mitscherlich  system  is  a  high 
tower,  usually  circular  in  section 
and  built  of  wood  or  of  cement 
lined  with  acid  resisting  tile. 
They  vary  from  6  to  10  feet  in 
diameter  and  from  100  to  150  feet 
in  height  and  generally  taper 
slightly  toward  the  top.  Fre- 
quently four  or  more  towers  are 
built  together  and  the  whole  sur- 
rounded with  a  wooden  structure 
with  stairs,  platforms  and  stone 
hoist.  A  water  tank,  supplied 
with  cold  water,  surmounts  each 
tower.  The  stone  is  supported 
on  strong  oak  beams  placed  about 
6  to  10  ft.  from  the  bottom  and 
below  these,  and  about  a  foot 
above  the  acid  outlet,  are  other 
beams  set  close  together  to  catch 
pieces  of  stone  which  pass  the 
upper  timbers.  Frequently  the 
tower  is  divided  into  sections 


\\V\V 

26.    MITSCHERLICH 
ACID  TOWER 


1 70  THE  SULPHITE  PROCESS 

by  timber  gratings  to  assist  in  the  filling  and  the  regulation  of  the 
absorption.  Some  towers  act  as  chimneys  and  no  artificial 
draft  is 'necessary  while  with  others  it  is  desirable  to  place  a  fan 
between  the  burners  and  the  towers  and  a  steam  exhaust  at  the 
top  of  the  towers. 

Ritter-Kellner  towers  are  constructed  in  pairs;  the  acid  from 
the  bottom  of  one  is  pumped  to  the  top  of  the  second  while  the 
gas  from  the  top  of  the  second  is  led  into  the  base  of  the  first. 
These  towers  are  smaller  than  the  Mitscherlich  towers  and  have 
the  advantage  of  avoiding  undue  loss  of  gas. 

Further  development  along  this  same  line  is  in  the  direction 
of  the  multiple  tower  system  where  towers  about  20  ft.  high  are 
worked  in  groups  of  six  to  eight.  The  acid  passes  through  these 
in  succession  in  one  direction  and  the  gas  in  the  other.  This 
system  is  easy  to  charge  with  stone,  and  permits  regulation  of 
the  gas  temperature  between  towers,  which  is  important  in 
maintaining  a  constant  ratio  of  base  to  acid.  Its  disadvantage 
lies  in  the  necessity  for  so  many  small  acid  pumps.  Such  a 
system  is  cheaper  to  install  but  more  costly  in  repairs  than  the 
high  tower  system,  and  the  latter  is  replacing  all  others  in 
European  plants. 

In  any  of  these  systems  the  towers  are  filled  with  lumps  of 
limestone  or  dolomite.  In  European  works  a  special  soft  lime- 
stone is  preferred  but  sufficiently  pure  material  of  this  nature  is 
not  available  in  this  country  and  ordinary  dense  stone  is  used. 
A  stone  low  in  magnesia  and  as  free  as  possible  from  dirt,  iron  and 
silica  is  preferred.  Since  marble'  is  practically  all  calcium  car- 
bonate and  is  of  uniform  structure  it  is  highly  satisfactory  for  use 
in  towers.  A  typical  analysis  of  a  suitable  stone  is  as  follows: 1 

Per  cent 

Loss  on  ignition 43-  63 

Iron  and  alumina o.  74 

Calcium  oxide 54- 10 

Magnesium  oxide 0.82 

Silica Q-59 

99-88 
1  Cooper:  Paper,  1918,  22,  721. 


ABSORPTION  APPARATUS  171 

The  water  is  discharged  over  the  stone  at  the  top  by  spray 
pipes  or  some  similar  device  and  in  passing  downward  forms  a 
thin  film  on  the  surface  of  the  lumps.  In  order  that  it  may  be 
properly  distributed  the  inside  of  the  tower  is  fitted  with  wooden 
rings  at  intervals  which  prevent  the  water  from  running  down 
the  walls  without  moistening  the  stones.  The  gas  from  the 
burners  enters  the  base  of  the  tower  under  the  grating  and  pass- 
ing upward  over  the  moist  limestone  is  very  rapidly  absorbed  by 
the  downward  flowing  film  of  water. 

In  working  with  tower  systems  several  difficulties  are  likely  to 
be  encountered.  It  is  hard  to  secure  a  uniform  distribution  of 
the  water  as  it  descends  the  tower  or  a  proper  spread  of  the  ascend- 
ing gas.  This  tends  to  form  channels  which  increase  rapidly 
after  their  first  appearance.  The  lower  lumps  of  stone  are  in 
contact  with  the  strongest  gas  and  so  dissolve  more  rapidly  than 
those  in  the  upper  part  of  the  tower;  this  tends  to  form  arches 
which  finally  break,  letting  the  stone  above  settle  so  compactly 
that  it  may  impede  the  passage  of  the  gas.  This  trouble  is  over- 
come in  modern  installations  by  tapering  the  tower  toward  the 
top,  by  dividing  it  into  sections  which  are  packed  with  stone 
separately  and  by  proper  periodical  inspection.  In  the  lower 
part  of  the  tower  crusts  of  sulphate  or  of  monosulphite  of  lime 
sometimes  almost  stop  the  flow  of  gas;'  the  latter  is  particularly 
apt  to  form  if  the  gas  is  weak  or  insufficient  water  is  used.  Irreg- 
ular acid  is  also  likely  to  result  if  the  temperature  varies  since, 
as  already  shown,  the  solubility  of  the  gas  decreases  rapidly  with 
rise  of  temperature  while  at  the  same  time  the  base  is  much  more 
quickly  dissolved  thus  changing  the  proportion  between  free  and 
combined  acid. 

Apparatus  for  use  in  acid  making  by  the  other  system,  where 
the  base  is  in  solution  or  suspension,  generally  consists  of  a 
series  of  tanks  with  accompanying  piping  or  in  other  installations 
of  towers  divided  into  sections  by  partitions.  A  frequent 
arrangement  consists  of  three  tight  tanks  fitted  with  agitators 
and  with  pipes  so  arranged  that  the  gas  enters  the  bottom  of  the 
first  tank  and  passes  upward  through  the  solution;  from  the 


172 


THE  SULPHITE  PROCESS 


ABSORPTION 

upper  part  of  this  tank  the  un- 
absorbed  gas  passes  to  the 
bottom  of  the  second  and  so 
on  through  the  system.  The 
gas  may  be  either  forced  in 
under  pressure  or  caused  to 
pass  through  by  an  exhaust 
fan  attached  to  the  last  tank. 
It  is  general  to  place  the  tanks 
at  different  levels  so  that  after 
drawing  off  the  finished  acid 
from  the  first  tank  the  contents 
of  the  second  and  third  may 
each  be  run  down  one  stage  by 
gravity.  Fresh  milk  of  lime 
is  charged  into  the  third,  or 
upper,  tank,  and  the  finished 
liquor  leaving  the  lower  tank 
should  be  quite  clear. 

The  Burgess  and  the  Barker 
systems  are  examples  of  the 
towerlike  form  of  tank  appa- 
ratus. The  Burgess  apparatus 
is  generally  one  high  tank  di- 
vided into  three  parts  by  hori- 
zontal partitions.  It  is  fitted 
with  a  hollow  shaft  and  arms 
through  which  the  gas  passes 
and  is  mixed  with  the  milk  of 
lime.  The  Barker  apparatus 
illustrated  in  its  relation  to  the 
other  equipment  in  Fig.  27,  is 
a  high  tank  divided  into  three 
or  more  compartments  by  hori- 
zontal perforated  partitions. 
The  construction  of  the  tower 
is  shown  in  Fig.  28.  The  milk 


APPARATUS 

5fcr/o/v  A- A 


173 


FIG.  28.    BARKER  TOWER, 
SECTIONAL  VIEW 


THE   SULPHITE   PROCESS 


of  lime  enters  the  upper  compartment  in  a  continuous  flow  and 
meets  the  gas  bubbling  up  through  the  perforated  false  bottom. 
The  weak  liquor  passes  through  an  overflow  pipe  to  the  next 
compartment  where  it  absorbs  more  gas,  and  so  on  through  the 
four  sections.  From  the  lowest  one  it  flows  onto  a  distributing 
plate  which  allows  it  to  trickle  down  into  the  absorbing  tower 
where  it  meets  strong  gas  and  is  strengthened  to  the  desired 
composition.  The  gas  enters  near  the  bottom  under  a  perforated 
distributing  plate  above  which  is  the  absorption  tower  filled  with 
stoneware  filling  to  increase  the  surface  exposed.  This  appa- 
ratus, as  well  as  any  good  tower  system,  working  in  conjunction 
with  a  proper  reclaiming  system,  will  produce  an  acid  with  i 
per  cent  combined  and  up  to  6  per  cent  total  S02. 

The  quality  of  the  lime  or  dolomite  used  for  liquor  making  is 
of  the  greatest  importance  and  its  value  increases  with  the 
amount  of  magnesia  which  it  contains.  For  use  in  milk  of  lime 
systems  it  should  be  well  burned,  should  slake  easily  and  should 
be  as  free  as  possible  from  silica  and  iron.  Air  slaked  or  poorly 
burned  limes  are  not  so  readily  acted  on  as  those  of  good  grade 
and  they  are  likely  to  vary  so  in  composition  that  it  is  almost 
impossible  to  keep  the  correct  proportion  of  base  to  acid.  The 
following  analyses  show  the  composition  of  several  extensively 
used  limes  from  different  parts  of  the  country. 


• 

Massachu- 
setts 

Ohio 

New 
Brunswick 

Calcium  oxide,  CaO                        / 

Per  cent 
^6  O2 

Per  cent 

«;8  61 

Per  cent 
ec   q6 

Magnesium  oxide,  MgO.  . 

40    IO 

4O    2< 

37   Q8 

Alumina  and  ferric  oxide,  AhQ3  and  Fe2Os.  . 
Sulphur  trioxide,  SO3.  

0-57 
O.  II 

O.I2 
O.  I<t 

1.23 
o  .  16 

Insoluble  in  HC1,  sand,  etc  

0.94 

O.Oy 

i  .  si 

Silica  soluble  in  acid,  SiO2 

O   47 

O    I  S 

i  81 

Loss  on  ignition,  H2O,  CO2,  etc  

i-43 

Q-51 

I  .00 

99-64 

99.86 

99-65 

It  frequently  happens  that  lime  of  the  above  quality  cannot 
be  obtained  on  time  so  that  it  is  necessary  to  use  high  calcium 


ABSORPTION  APPARATUS  175 

lime  for  a  certain  period.  It  has  been  found  by  experience  with 
the  Barker  system  that  this  causes  no  serious  inconvenience  nor 
does  it  require  any  radical  change  in  the  cooking  system.  The 
opinion  seems  to  be  gaining  ground  that  a  high  calcium  lime  can 
be  used  in  the  milk  of  lime  system  with  practically  the  same  results 
as  with  dolomitic  lime. 

Lime  for  use  in  the  absorption  system  is  first  slaked  either  in 
tanks  provided  with  agitators  or  in  troughs.  One  authority 
recommends  a  tank  with  a  perforated  plate  on  which  the  lime  is 
dumped  after  filling  the  tank  with  water  to  one  inch  above  the 
surface  of  the  plate.  The  lime  is  sprinkled  on  top  with  water 
and  when  it  steams  freely  is  quickly  covered  with  water.  'The 
milk  of  lime  produced  is  diluted  sufficiently  so  that  it  can  be 
strained  through  brass  sieves  of  60  meshes  to  the  inch  and  the 
strained  material  run  to  storage  tanks  fitted  with  agitators  where 
it  is  diluted  to  the  proper  consistency.  The  milk  of  lime  must 
be  cold  when  it  goes  to  the  absorption  system.  According  to 
Beveridge  1  the  finished  milk  of  lime  has  a  specific  gravity  of 
1.0075  and  contains  6.31  gms.  per  liter  of  CaO  and  4.19  gms. 
per  liter  of  MgO.  This  corresponds  to  about  91  Ibs.  of  lime  of 
the  composition  given  to  a  thousand  gallons  of  acid.  As  the  lime 
is  never  entirely  dissolved  and  some  is  lost  as  sulphate  and  mono- 
sulphite  in  cleaning  the  apparatus  more  than  the  above  quantity 
has  to  be  used,  the  amount  depending  on  the  quality  of  the  lime, 
the  type  of  apparatus,  etc. 

There  is  still  iriuch  dispute  as  to  the  relative  advantages  of  the 
tower  and  milk  of  lime  systems.  The  latter  are  no  longer  com- 
mon in  Europe  where  towers  are  generally  employed,  but  they 
are  much  used  in  America.  The  advocates  of  the  tower  systems 
claim  that  they  are  simpler  to  operate,  require  less  power  and  cost, 
less  for  upkeep.  The  cost  of  lime  is  also  less  as  the  unburned 
stone  is  cheaper  than  burned  lime.  Obermanns 2  states  that, 
towers  require  50  to  60  horse  power  as  compared  with  225  horse 
power  for  a  three  tank  system,  and  that  the  sulphur  per  ton  of 

1  Beveridge:  Paper  Makers'  Pocket  Book,  p.  99. 

2  Obermanns:  Paper,  1918,  Feb.  13,  p.  100. 


176  THE  SULPHITE  PROCESS 

pulp  is  240  Ibs.  as  against  300  Ibs.  for'the  tank  system.  For  a 
loo-ton  mill  these  savings,  together  with  that  for  the  cheaper 
lime,  would  amount  to  $42,000  to  $52,000  per  year.  Textor1 
compared  the  systems  from  a  thermochemical  standpoint  and  con- 
cludes that  an  acid  of  2.00  per  cent  free  and  1.60  per  cent  com- 
bined SO2  will  entail  a  rise  of  6.4°  C.  if  made  in  towers  from  cal- 
cite,  and  16.1°  C.  if  made  in  a  milk  of  lime  system  from  a  high 
magnesia  lime  without  the  use  of  steam  in  slaking  or  of  cooling 
water  in  making  up  the  tanks.  Considering  the  claim  that 
towers  produce  stronger  acid  it  is  to  be  noted  that  they  operate 
at  nearly  atmospheric  pressure  whether  the  gas  is  passed  through 
by  pressure  or  vacuum.  Tank  systems,  such  as  the  Barker,  gen- 
erally operate  by  means  of  a  vacuum  pump  and  if  this  were 
changed  to  force  the  gas  through  under  pressure  the  strength  of 
the  acid  would  be  increased  by  1 5  to  20  per  cent. 

The  losses  which  occur  in  making  sulphite  liquor  are  those  due 
to  dirt,  ash  and  moisture  in  the  sulphur,  to  sublimation,  and  to 
the  formation  of  sulphuric  acid.  The  loss  from  the  first  four 
causes  should  never  exceed  5  per  cent,  but  that  from  formation 
of  sulphuric  acid  is  likely  to  amount  to  very  much  more  unless 
careful  control  is  maintained.  The  formation  of  monosulphite, 
which  is  removed  with  the  sediment  in  the  storage  tanks  or  in 
cleaning  the  absorption  system,  may  also  cause  considerable  loss. 
Such  wastes  should  be  examined  before  being  thrown  away  as 
it  often  pays  to  work  them  over. 

The  acid  made  in  either  the  tower  or  the  tank  system  varies 
very  widely  in  different  mills  according  to  the  kind  of  fibre  being 
made  and  the  method  of  enriching  the  liquor  with  the  relieved  or 
recovered  gas.  There  is  no  essential  difference,  however,  between 
the  two  systems  with  regard  to  the  liquor  produced.  Harpf 2 
gives  the  composition  of  liquor  of  4.5°  Be.  from  Mitscherlich 
towers  as  follows: 

Per  cent 

Total  SO2 -. .  . .     3-397 

Free  SO2 2. 098 

Combined  SO2 i.  299 

1  Textor:  Paper,  1918,  Feb.  13,  p.  60.          2  Harpf:  Dissertation,  1892. 


PUMPING  AND   STORAGE 


177 


The  acid  from  either  tower  or  tank  system  is  stated  by  Thorne  l 
to  have  the  following  composition  before  being  enriched  by  the 
recovered  gas. 

Per  cent 

Total  SO2 2.  60 

Free  SO2 i.  60 

Combined  SO2 i. oo 

The  finished  acid  when  ready  for  the  digesters  is  also  very  variable 
in  strength.  From  reports  on  a  number  of  American  mills  the 
following  figures  have  been  selected  as  representative: 


i 

2 

3 

4 

5 

Total  SO2  

Per  cent 

4   3O 

Per  cent 
4  -OQ 

Per  cent 
^  .  <?O 

Per  cent 
3.80 

Per  cent 
6  .24 

Free  SO2  

3  .  IO 

2  .46 

4  •  5O 

2  .40 

5-22 

Combined  SO2  

I  .20 

1.63 

I  .OO 

I  .40 

I  .02 

Acid  of  the  strength  of  No.  5  can  only  be  obtained  during  warm 
weather  by  employing  artificial  refrigeration;  in  this  particular 
case  the  temperature  of  the  acid  ready  for  the  digesters  was  72°  F. 
(22.2°  C.). 

Pumping  and  Storage.  Where  the  liquor  is  to  be  discharged 
directly  into  the  digester,  a  steam  injector  may  be  used  for 
transferring  it,  but  if  nothing  is  to  be  gained  by  heating  the  liquor 
an  injector  is  too  expensive  and  it  also  causes  considerable  loss 
of  sulphurous  acid.  The  best  method  of  handling  is  with  rotary 
pumps  of  acid-resisting  bronze,  which  should  be  so  placed  that 
the  acid  flows  to  them  under  a  slight  head.  If  a  pump  is  so 
placed  that  a  foot- valve  is  necessary  on  the  suction  pipe  continual 
trouble  will  be  caused  by  the  crystallization  of  monosulphite  in 
the  working  parts. 

Storage  tanks  for  liquor  are  generally  of  wood,  either  Southern 
pine  or  Douglas  fir,  without  lining.  They  should  be  made  tight 
with  water  or  steam  before  any  liquor  is  admitted  so  that  no 
monosulphite  may  crystallize  between  the  staves.  The  tanks 

1  Thorne:  Pulp  Paper  Mag.  Can.,  March  15,  1915,  p.  173. 


i78 


THE  SULPHITE  PROCESS 


should  be  covered  to  prevent  escape  of  gas  but  the  covers  need 
not  be  perfectly  air-tight  since  there  is  little  loss  in  strength, 
either  through  escape  of  gas  or  oxidation  to  sulphate,  when  the 
liquor  is  stored  in  quantity.  The  tanks  should  be  fitted  with 
gauge  glasses  to  show  the  depth  of  liquid  and  the  delivery  pipes 
should  draw  from  near  the  bottom  but  high  enough  to  avoid 
sediment.  The  tanks  should  be  so  located  that  the  sediment 
may  be  easily  washed  out  when  necessary. 

Digesters  and  Digester  Linings.  The  acid  liquor  used  in 
the  sulphite  process  acts  so  destructively  on  iron  that  some  form 
of  lining  is  necessary  to  protect  the  digester  shell.  According  to 
Griffin  and  Little  1  wrought  iron  suffers  most  severely,  steel 
resists  somewhat  better  and  cast  iron  suffers  least  of  all.  Even 
the  modern  acid-resistant  cast  irons,  which  are  extensively  used 
in  concentrating  acids,  have  proved  to  be  too  easily  attacked  to 
be  safe  for  use  in  the  sulphite  industry.  Tests  by  the  author  on 
a  number  of  such  cast  irons  gave  the  following  results : 


Loss  in  grams  per  square  inch 

18  hours  in 
cold 

4  hours  more 
at  90°  C. 

18  hours  more 
in  cold 

Ordinary  cast 
Acid  resistant 
Acid  resistant 
Acid  resistant 
Acid  resistant 

iron  
No.  i  . 

0.6410 
0.2615 
0.2362 
,  0.3275 
0.5410 

0.1096 
0.0990 
0.2138 

o  .  2030 
0.1184 
0.1797 

No.  2  .  . 

No.  3  
No.  4  

Lead  is  the  only  common  metal  which  satisfactorily  resists  the 
action  of  the  acid  liquor  and  this  is  due  very  largely  to  the 
formation  of  a  surface  film  of  insoluble  lead  sulphate  which  acts 
as  a  protective  coating  for  the  metal  beneath.  Lead,  however, 
has  certain  properties  which  have  prevented  its  successful  use  in 
digester  lining  in  spite  of  the  immense  amount  of  time  and  money 
which  have  been  spent  in  the  attempt.  Its  coefficient  of  expan- 
sion is  0.0000297  while  that  of  iron  is  only  0.0000123,  so  that  on 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  232. 


DIGESTERS   AND   DIGESTER  LININGS  179 

heating  the  digester  the  lead  lining  tends  to  become  too  large  for 
the  shell.  This  trouble  is  still  further  increased  by  the  fact  that 
lead  which  has  been  expanded  by  heat  does  not  quite  return  to 
its  original  size  on  cooling  but  remains  permanently  larger.  This 
causes  "  crawling"  and  "  buckling"  and  cracks  are  apt  to  appear 
j  wherever  short  turns  are  made.  There  is  also  in  vertical  digesters 
a  gradual  creeping  downward  of  the  lead  due  to  its  own  weight; 
this  causes  the  upper  part  to  become  thinner  and  finally  give 
way.  Even  uniting  the  lead  to  the  iron  by  melting  it  on  over  a 
flux  of  zinc  chloride,  a  true  soldering  process,  did  not  prove 
entirely  satisfactory.  Griffin  1  states  that  such  linings  remained 
clean  until  about  two  hundred  cooks  had  been  made,  then  star- 
shaped  defects  showing  cracks  and  hard  crystals  appeared  and 
multiplied  so  fast  that  they  could  not  be  cut  out  and  repaired. 
Finally  black  scabs  of  lead  sulphide  formed  in  large  masses  and 
the  whole  lining  became  worthless.  Many  other  very  ingenious 
methods  for  controlling  the  lead  were  tried  but  the  task  was 
finally  given  up  as  hopeless. 

Bronze  digesters,  built  of  cast  sections,  were  tried  at  one  time 
but  were  found  to  be  more  or  less  acted  on  by  the  liquor  with 
the  formation  of  black  scales  of  oxide  and  sulphide  of  copper. 
Heating  to  the  temperatures  used  in  cooking  considerably  re- 
duces the  strength  of  bronze  and  after  several  disastrous  explo- 
sions the  use  of  such  digesters  was  abandoned. 

The  Salomon-Briingger  digester  consisted  of  an  inner  shell  of 
welded  steel  and  an  outer  shell  also  of  steel  but  riveted.  The 
protective  coating  is  obtained  by  admitting  sulphite  liquor  into 
the  digester  which  has  been  previously  heated  by  steam  in  the 
jacket  at  about  40  Ibs.  pressure.  This  treatment  causes  the 
deposit  of  a  hard,  impervious  crust  of  sulphite  of  lime  which 
gradually  increases  in  thickness  with  each  succeeding  cook. 
This  coating  did  not  prove  to  give  adequate  protection  and  the 
method  was  never  in  extensive  use. 

The  Mitscherlich  lining  is  interesting  as  being  the  first  in 

1  M.  L.  Griffin:  J.  Soc.  Chem.  Ind.,  1898,  216-220. 


180  THE  SULPHITE  PROCESS 

which  bricks  were  used.  It  consists  first  of  a  coating  of  tar 
and  pitch  applied  directly  to  the  shell,  then  a  thin  lining  of 
sheet  lead  with  the  edges  burned  together  and  finally  two 
courses  of  dense  vitrified  bricks  with  tongues  and  grooves. 
These  were  sometimes  laid  in  Portland  cement. 

The  Preston  lining  consists  of  bricks  of  Scottish  clay  backed 
with  a  mixture  containing  clay  and  lead  mixed  to  the  consistency 
of  bread  dough  with  silicate  of  soda.  This  must  be  applied  to  a 
perfectly  clean  shell. 

Modern  digester  linings  are  generally  of  acid-proof  bricks 
backed  with  cement  next  to  the  shell.  The  bricks  are  2  to  3  ins. 
thick  while  the  cement  backing  is  about  an  inch  thick.  In  some 
cases  a  lead  lining  is  applied  next  the  shell  and  upon  this  the  ce- 
ment backing  is  laid.  This  is  seldom  done,  however,  as  it  is  cus- 
tomary to  pierce  the  digester  shell  with  numerous  small  tell-tale 
holes  so  that  the  location  of  cracks  in  the  lining  may  be  approxi- 
mately known.  The  cement  for  the  backing  and  pointing  the 
first  layer  of  bricks  varies  more  or  less  in  different  localities. 
Steffanson  1  gives  its  composition  as  one  part  of  cement,  and  two 
parts  of  crushed  and  sifted  acid-proof  brick  with  enough  asbes- 
tos added  to  render  it  non-brittle;  this  is  mixed  to  the  desired 
consistency  with  4°  Be.  silicate  of  soda.  The  last  layer  of  bricks 
is  pointed  with  litharge  and  glycerine  and  the  bricks  should  be 
set  half  an  inch  apart  to  make  repairs  easy.  Another  formula 2 
for  pointing  the  inner  layer  of  bricks  is  5  parts  litharge,  2  parts 
cement  and  3  parts  quartz  sand,  all  measured  by  volume.  After 
mixing  these  materials  dry,  they  are  moistened  with  glycerine 
to  the  right  consistency  for  use.  This  should  be  mixed  in  small 
quantities  only  and  used  quickly  as  the  mixture  retains  the 
proper  consistency  for  only  a  short  time.  Digesters  pointed 
with  this  mixture  have  been  operated  up  to  eighteen  months 
without  repairs  and  in  some  cases  the  pointing  has  proved  more 
durable  than  the  bricks  so  that  the  latter  have  worn  down, 
leaving  a  raised  network  of  cement  exposed. 

1  Steffanson:  Pulp  Paper  Mag.  Can.,  May  20,  1914,  et  seq. 

2  Private  communication. 


DIGESTERS   AND   DIGESTER  LININGS  l8l 

The  bricks  used  for  digester  lining  should  be  very  hard,  dense 
and  well  annealed.  If  soft  or  under-burned  they  are  apt  to 
crack  from  changes  in  temperature  and  pieces  then  come  away 
in  the  pulp.  When  tested  by  immersing  in  water  for  twenty-four 
hours  they  should  not  absorb  more  than  2  per  cent  of  their 
weight. 

In  general  the  form  of  digester  used  is  that  of  a  vertical  cyl- 
inder with  conical  top  and  bottom.  The  total  length  is  about 
three  times  the  diameter,  and  the  lower  cone  is  about  60  degs. 
while  the  upper  is  about  no  degs.  Digesters  of  other  forms 
are  of  course  used  in  some  of  the  older  mills  and  horizontal 
digesters  are  sometimes  used  for  the  Mitscherlich  process.  The 
size  of  digesters  has  gradually  increased;  formerly  a  capacity 
of  4  tons  of  fibre  per  charge  was  considered  large  while  now  18 
tons  or  more  is  not  uncommon.  The  following  table  by  Cor- 
coran 1  gives  the  approximate  capacities  of  sulphite  digesters  of 
standard  construction  and  lined  with  the  usual  brick  and  cement 
lining: 

1  Corcoran:  Paper,  22,  1918,  406. 


182 


THE  SULPHITE  PROCESS 


CAPACITY  OF  STANDARD  SULPHITE  DIGESTERS  WITH  STANDARD  LININGS 


Size  of  digester 

Thickness 
of  lining, 
ins. 

Contents, 
CU.  ft. 

Capacity 
contents, 
tons  fibre 

Gallons  of 
acid 

Cords  of 
wood 

Diameter, 
ft. 

Height, 
ft. 

8 

24 

8 

610 

1-33 

3,000 

2.48 

8 

30 

8 

840 

1-75 

3,787 

3-24 

10 

28 

8 

i.3i9 

2.66 

6,000 

4-96 

10 

30 

8 

1.397 

2.90 

6,525 

5-34 

IO 

37 

8 

1,850 

3-85 

8,663 

7.16 

IO 

40 

8 

2,024 

4-50 

9,450 

7.81 

II 

30 

8 

1,672 

3-48 

7,330 

6-47 

II 

37 

8 

2,896 

4.60 

10,125 

8-37 

II 

40 

8 

2,416 

5-oo 

11,250 

9-30 

II 

42 

8 

2,563 

5-33 

12,000 

9-92 

II 

45 

8 

2,784 

5-75 

12,937 

10.69 

12 

30 

9 

2,015 

4-13 

9,282 

7-67 

12 

35 

9 

2,457 

5-10 

11,470 

9-48 

12 

40 

9 

2,879 

6.00 

13,500 

ii  .16 

12 

45 

9 

3,272 

6.80 

15.300 

11.64 

12 

48 

9 

3,572 

7.40 

16,650 

13.76 

14 

38 

9 

3,8i9 

7-90 

17,775 

14.64 

14 

42 

9 

4,320 

9.00 

20,250 

16.74 

14 

45 

9 

4,678 

9-75 

2i,934 

18.13 

14 

47 

9 

4,924 

10.50 

22,950 

18.97 

14 

48 

9 

5,046 

10.64 

23,625 

19-53 

14 

50 

9 

5,392 

II  .20 

25,000 

20.83 

15 

40 

IO 

4,682 

9-75 

2i,934 

18.13 

15 

42 

IO 

4,964 

10.33 

23,250 

19.22 

15 

45 

IO 

5,388 

ii  .20 

25,200 

20.83 

15 

47 

IO 

5,67i 

n.  80 

26,550 

21.31 

15 

So 

10 

6,096 

12  .40 

27,900 

22  .06 

15 

54 

10 

6,652 

13-75 

30,937 

25-57 

16 

45 

IO 

6,146 

12.  80 

28,800 

24.80 

16 

48 

IO 

6,680 

13-75 

30,937 

25-57 

16 

50 

IO 

6,952 

14.40 

32,400 

26.78 

16 

54 

IO 

7,598 

15.80 

35,550 

29.38 

16 

60 

IO 

8,565 

17.80 

40,050 

33-10 

16 

64 

IO 

9,210 

19.00 

42,750 

35-34 

i7 

56 

10 

9.074- 

18.80 

42,300 

34.96 

17 

60 

IO 

9,814 

20.25 

45,9oo 

37-94 

17 

64 

IO 

i°,552 

21.80 

49.050 

40.44 

17 

70 

IO 

i  i,  660 

23.00 

5i,75o 

42.78 

The  digester  space  required  to  produce  2000  Ibs.  of  dry  pulp 
is  given  by  Steffanson  as  follows: 

Cu.ft. 

Mitscherlich  process 400-425 

Quick  cook  process 450 

For  easy  bleaching  pulp 475-500 


BOILING  183 

Boiling.  The  method  of  making  a  boil  depends  on  whether 
the  Mitscherlich  or  the  quick  cook  process  is  being  employed. 
The  former  is  very  generally  used  in  Europe  but  in  America  is 
not  nearly  so  common  as  the  quick  cook  or  Ritter-Kellner 
process. 

In  the  Mitscherlich  process  the  digesters  are  either  horizontal 
or  vertical  stationary  boilers.  The  cooking  is  all  done  by  steam 
admitted  to  coils  of  hard  lead  or  copper  pipe  placed  in  the  bot- 
tom of  the  digester.  The  standard  procedure  is  to  fill  the 
digester  with  chips  and»  then  steam  gently  for  several  hours 
with  direct  steam,  the  water  condensing  being  allowed  td  run 
to  waste  as  a  brownish  liquid.  Care  must  be  used  during  this 
period  to  avoid  steam  pressure  in  the  digester  as  temperatures 
much  in  excess  of  100°  C.  are  likely  to  burn  the  wood.  After 
steaming  all  valves  except  that  leading  to  the  liquor  tanks  are 
closed  and  the  partial  vacuum  formed  by  the  cooling  of  the 
digester  and  the  condensation  of  the  steam  draws  the  cold 
liquor  in  rapidly.  The  object  of  this  steaming  and  subsequent 
admission  of  cold  liquor  is  to  obtain  thorough  penetration  of 
the  chips  by  the  liquor  and  so  prevent  floating  and  burning. 
Steam  is  now  admitted  to  the  coils  and  the  temperature  raised 
to  110°  C.  as  rapidly  as  possible,  although  this  may  require  as 
much  as  twelve  hours  because  of  the  large  size  of  the  digester. 
When  pressure  is  reached  it  is  relieved  by  opening  a  valve  for 
a  few  minutes  to  get  rid  of  air;  this  is  repeated  two  or  three 
times  in  the  next  hour.  Since  the  relief  from  Mitscherlich 
cooks  contains  no  liquor  no  separator  is  necessary  and  the 
relieved  gas  can  go  at  once  to  the  reclaiming  system.  The 
temperature  in  the  digester  is  gradually  raised  to  about  120°  C. 
which  is  maintained  throughout  the  cooking  period;  during 
this  time  the  pressure  should  not  exceed  80  Ibs.  About  an 
hour  before  the  end  of  the  cook  the  steam  is  shut  off  and  the 
pressure  gradually  reduced  to  50  Ibs.  by  relieving  gas;  this 
must  not  be  done  too  rapidly  or  the  pulp  may  not  be  thoroughly 
reduced  by  the  time  the  sulphur  dioxide  is  gone.  The  contents 
of  the  digester  are  then  discharged  as  usual.  The  old  method 


1 84  THE  SULPHITE  PROCESS 

of  emptying  horizontal  digesters  was  to  admit  cold  water  as 
soon  as  the  liquor  had  been  discharged,  the  object  being  to  cool 
and  wash  the  pulp  which  was  finally  removed  by  shovelling. 

The  liquor  used  in  the  Mitscherlich  process  is  about  3.5  to 
4.5  per  cent  total  $0%  with  0.9  to  1.24  per  cent  combined.  The 
steam  used  in  the  coils  is  at  60  to  100  Ibs.  pressure:  75  Ibs.  in 
the  coils  gives  about  90  Ibs.  in  the  digester.  The  actual  time 
of  cooking  varies  enormously  in  different  mills.  It  was  origi- 
nally about  eighty  hours,  but  this  has  been  greatly  reduced  by 
raising  the  temperature  of  cooking  and  by  using  some  direct 
steam  to  bring  the  charge  up  to  pressure  quickly.  In  this 
latter  case  space  must  be  left  in  the  digester  to  allow  for  con- 
densation. In  modern  practice  the  total  time  is  about  twenty- 
five  to  forty-five  hours.  Steffanson  *  states  that  for  bleached 
pulp  the  cook  is  usually  not  more  than  twenty-four  hours,  while 
Beveridge  2  subdivides  the  time  as  follows  for  a  digester  which 
has  to  be  emptied  by  hand. 

Hours 

Filling 2 

Steaming 4 

Filling  with  liquor 2 

Boiling 35 

Blowing  off  pressure 3 

Washing  twice 6 

Emptying,  etc 5 

Total ^ 

The  particular  advantages  of  the  Mitscherlich  process  are 
strong  fibre  and  high  yield  because  of  the  comparatively  weak 
acid  and  the  low  temperature  .of  cooking.  It  is  stated  by, 
Bache-Wiig3  that  temperatures  over  135°  C.  cause  the  forma- 
tion of  hydrocellulose  with  consequent  lower  yield  and  loss  of 
strength. 

The  Ritter-Kellner,  or  quick  cook  process,  in  which  the  steam 
is  blown  directly  into  the  digester,  is  the  one  most  generally 

1  Steffanson:  Pulp  Paper  Mag.  Can.,  May  20,  1914,  et  seq. 

2  Beveridge:  Paper  Makers'  Pocket  Book. 

3  Private  communication. 


BOILING  185 

used  in  this  country.  The  digester  is  usually  charged  with 
chips  as  fully  as  possible  since  the  settling  during  the  first  part 
of  the  cook  suffices  to  cover  them  completely  with  liquor.  Steam- 
ing of  the  chips  is  seldom  resorted  to,  though  it  is  an  advantage, 
as  it  drives  out  air,  moistens  the  chips  uniformly  and  makes 
better  pulp.  Moreover  the  partial  vacuum  formed  in  the 
digester  when  steam  is  shut  off  hastens  the  running  in  of  the 
acid  and  makes  it  possible  to  perform  this  operation  without 
removing  the  digester  head.  The  most  satisfactory  point  to 
admit  the  acid  is  at  the  bottom  of  the  digester;  if  pumped  in 
from  below  instead  of  on  top  of  the  chips  it  tends  to  loosen 
them  up  and  helps  the  circulation.  The  steam  inlet  for  'cook- 
ing generally  ends  in  a  coil  around  the  sides  near  the  bottom 
and  is  perforated  in  such  a  way  as  to  direct  the  steam  up  the 
sides,  thus  giving  a  downward  current  in  the  center  and  good 
circulation.  There  is  also  provided  a  small  jet  just  at  the 
bottom  of  the  digester  to  cook  the  chips  in  the  lower  part  of 
the  bottom  cone. 

The  steam  used  in  cooking  may  be  superheated  or  ordinary 
saturated  steam,  the  latter  being  used  in  far  the  greater  num- 
ber of  cases.  Tests  by  Andrews  1  using  superheated  steam  with 
a  temperature  of  500°  F.  at  the  digesters  indicated  that  it  gave 
a  little  more  uniform  product  and  that  a  somewhat  stronger 
acid  could  be  prepared.  No  difference  in  yield  could  be  de- 
tected and  the  volume  of  liquor  and  the  fuel  required  were  the 
same  as  with  saturated  steam. 

The  steam  required  for  cooking  is  much  greater  than  for  a 
soda  cook  of  a  corresponding  number  of'  cords.  This  is  due  to 
the  continual  relief  of  gas  and  steam  through  the  coolers  into 
the  recovery  system.  Andrews  calculates  the  saturated  steam 
for  a  14  X  47  ft.  digester  holding  16  cords  of  rossed  wood  as 
about  60,000  Ibs.  per  cook.  In  another  plant  with  digesters  of 
about  the  same  capacity  steam  flow  meter  records  during  a 
period  of  four  months  showed  that  the  average  steam  consump- 
tion per  cook  was  75,940  Ibs. 

1  Andrews:  Paper,  Feb.  20,  1918. 


1 86  THE  SULPHITE  PROCESS 

In  steaming  a  cook  it  is  very  important  that  the  pressure  be 
brought  up  slowly  as  otherwise  a  high  temperature  may  be 
reached  before  the  liquor  has  had  time  to  penetrate  the  chips 
and  their  centers  will  be  found  hard  and  of  a  red  or  brown 
color.  The  time  from  the  start  until  75  Ibs.  pressure  is  reached 
varies  in  different  mills  from  two  to  four  hours.  The  pressure, 
however,  does  not  afford  a  reliable  indication  of  conditions 
within  the  digester  since  the  actual  steam  pressure  is  augmented 
by  that  of  the  gas  set  free  during  boiling  and  in  some  cases  the 
indicated  pressure  may  be  almost  wholly  hydrostatic  due  to  the 
filling  of  the  digester  by  condensation.  The  temperature  is 
therefore  the  real  factor  to  be  watched  and  this  should  be  taken 
at  a  point  about  one-third  of  the  way  down  the  digester.  The 
best  method  of  keeping  track  of  the  temperature  is  by  means  of. 
some  form  of  recording  thermometer  as  this  gives  a  permanent 
record  of  each  cook  from  start  to  finish. 

No  hard  and  fast  rule  for  cooking  can  be  given  and  each  mill 
has  its  own  particular  method  which  is  generally  the  result  of 
gradual  evolution  rather  than  the  application  of  scientific  knowl- 
edge. As  an  example  of  the  procedure  in  cooking  easy  bleach- 
ing pulp  of  high  quality  Steffanson  1  gives  the  following  schedule: 
Steam  in  such  a  way  as  to  reach  75  Ibs.  pressure  in  two  to  three 
hours;  open  relief  and  bring  temperature  to  240°  F.  (115.5°  C.) 
in  about  an  hour.  Close  both  steam  and  relief  valves  for  an 
hour  and  a  half,  then  turn  on  steam  and  open  relief  very 
slightly.  The  maximum  temperature  of  300°  F.  (149°  C.)  should 
be  reached  in  ten  hours  with  the  maximum  pressure  still  75  Ibs. 
Now  shut  off  steam  but  not  relief,  allow  the  pressure  to  drop  to 
50  Ibs.  in  one  to  two  hours  and  discharge  into  the  blowpits. 
At  the  end  of  the  cook  the  liquor  should  test  0.05  per  cent 
total  S02.  If  the  cook  is  blown  at  a  pressure  much  in  excess  of 
50  Ibs.  some  partially  cooked  chips  will  be  blown  to  pieces  and 
cause  shives. 

1  Steffanson:  Pulp  Paper  Mag.  Can.,  May  20,  1914,  et  seq. 


BOILING 


I87 


In  another  mill  making  an  easy  bleaching  sulphite  for  use 
in  writing  papers  the  following  schedule  is  in  effect: 

Bring  to  78  Ibs.  pressure  in  three  hours  and  then  start  relief. 

Bring  temperature  to  228°  F.  at  4th  hour. 

Bring  temperature  to  246°  F.  at  5th  hour. 

Bring  temperature  to  262°  F.  at  6th  hour. 

Bring  temperature  to  278°  F.  at  7th  hour. 

Bring  temperature  to  290°  F.  at  8th  hour. 

Bring  temperature  to  298°  F.  at  9th  hour. 

Start  to  reduce  pressure  when  5  c.c.  of  liquor  require  2,j  c.c. 
of  iodine  and  lower  to  50  Ibs.  at  blow,  which  is  when  5  c.c.  of 
liquor  require  0.7  c.c.  of  iodine. 

Fig.  29  shows  the  general  method  of  recording  the  conditions 


10 


11        12 


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80 

4 

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70 

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a 

5- 

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^ 

i 

ou 

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^ 

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50 

t 

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2 

/ 

1 

\ 

8 

! 

a 

r. 

40 

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3C 

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20 

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-N; 

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V 

0 

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Time 
FIG.  29.    SULPHITE  COOKING  CHART 


within  the  digester  during  the  cook.     Observations  are  taken 
at  frequent  intervals  and  plotted  on  the  chart  in  such  a  way  as 


1 88  THE   SULPHITE  PROCESS 

to  show  the  gauge,  gas  and  steam  pressures.  This  gives  a  graphic 
representation  which  can  be  followed  easily  by  the  workmen. 
The  chart  given  is  for  a  quick  cook  easy-bleaching  sulphite. 
Fig.  30  is  the  temperature  record  taken  during  such  a  cook. 

During  the  progress  of  a  cook  the  heat  and  the  chemical  re- 
actions taking  place  within  the  digester  cause  more  or  less  gas 


m 

r.  i$^e    /          I 


FIG.  30.     TEMPERATURE  RECORD  OF  A  SULPHITE  COOK 

to  be  evolved  which  results  in  a  gradual  building  up  of  the  pres- 
sure. This  gas  pressure  is  not  injurious  to  the  fibre  provided 
the  temperature  is  carried  at  the  right  point,  but  it  is  the  general 
custom  to  reduce  it  by  "relieving"  or  blowing  off  some  of  the 
gas  either  at  intervals  or  continuously.  Study  by  Schwalbe  x  of 

1  Schwalbe:  Wochbl.  Papier-Fabr.,  1913,  44,  2786. 


RELIEVING  GAS  189 

the  relieved  gases  shows  that  when  blown  off  at  110°  C.  they 
contain  no  oxygen,  indicating  that  all  originally  present  in  the 
digester  has  already  been  used  up.  He  recommends  relieving 
air  when  the  temperature  reaches  75°  C.  as  the  bisulphite  is 
relatively  stable  at  that  temperature  and  the  loss  of  gas  will 
consequently  be  less.  The  relief  at  times  also  contains  much 
liquor  and  for  this  reason  it  is  sometimes  passed  through  a 
separator  of  some  kind  so  that  the  gaseous  portion  may  be  con- 
veyed to  the  liquor  tanks  to  bring  up  the  strength  of  the  raw 
acid  to  the  proper  cooking  strength.  This  recovery  process  is 
of  the  first  importance  in  reducing  the  consumption  of  sulphur 
per  ton  of  pulp.  The  amount  of  relief  depends  partly  on  the 
strength  of  the  acid  used  since  the  stronger  the  acid  the  greater 
will  be  the  amount  of  gas  evolved  on  heating.  The  kind  of 
cook,  direct  or  indirect  steam,  and  the  temperature  of  cooking 
also  have  much  influence  on  the  amount  of  relief.  If  too  much 
gas  is  blown  off  the  pulp  will  be  burned  and  whenever  burned 
pulp  is  obtained  and  the  temperature  has  not  risen  above  320°  F. 
(160°  C.)  it  is  an  indication  that  the  acid  was  originally  too 
weak  or  that  too  much  gas  was  blown  off.1  If  it  is  discovered 
during  a  cook  that  the  usual  method  of  relief  will  allow  too 
much  S02  to  escape  before  the  cook  is  done  it  may  be  remedied 
by  closing  the  relief,  drawing  off  some  of  the  liquor  from  the 
bottom  of  the  digester,  and  then  again  steaming.  Some  mills 
use  this  method  regularly,  relieving  only  to  get  rid  of  air  and  to 
reduce  pressure  before  blowing.2 

In  practice  the  relieving  of  a  digester  is  done  from  one  or 
both  of  two  points,  either  through  the  top  or  through  the  side. 
It  is  claimed  by  Wimmer  3  that  side  relief  is  a  help  in  systematic 
cooking  and  also  aids  in  the  recovery  of  gas  and  the  reduction 
of  sulphur  per  ton  of  pulp.  To  use  the  side  relief  to  the  best 
advantage  he  recommends  relieving  from  the  top  for  about  one 
and  one-half  to  two  hours,  or  until  the  temperature  is  120°  to 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  252. 

2  Steffanson:  Paper,  June  3,  1914,  p.  19. 

3  Wimmer:  Paper,  Jan.  19,  1916,  15. 


190  THE  SULPHITE  PROCESS 

130°  C.  (248°  to  266°  F.),  then,  closing  the  top  entirely,  relieve 
from  the  side  for  one  and  one-half  to  two  hours.  After  this  top 
relief  can  be  started  again  and  only  dry  gas  will  ordinarily  be 
obtained  to  the  end  of  the  cook.  On  large  digesters  there 
should  be  from  three  to  five  hours  of  dry  gas. 

As  already  stated  the  composition  of  the  acid  liquor  varies 
greatly  in  different  mills  and  with  the  nature  of  the  fibre  being 
made.  Schlick  l  states  that  the  strength  of  the  pulp  produced 
is  in  indirect  proportion  to  the  strength  of  the  acid  used.  Ex- 
periments by  the  Forest  Products  Laboratory  2  appear  to  indi- 
cate that  with  a  total  S02  content  of  5  per  cent,  increasing  the 
amount  of  combined  S02  above  i.o  per  cent,  has  very  little 
influence  on  the  time  of  cooking  while  decreasing  the  combined 
acid  below  i.o  per  cent  increases  the  speed  of  cooking.  As  the 
combined  S02  is  decreased  below  i  per  cent  there  is  an  increase 
in  the  amount  of  screenings  and  in  the  bleach  required.  Other 
authorities  place  the  lower  limit  for  combined  S02  at  0.75  per 
cent  and  agree  that  going  below  this  point  increases  the  bleach 
required.  Decreasing  the  temperature  of  cooking  between  the 
limits  of  146°  C.  and  110°  C.  tended  to  increase  the  yield  and 
decrease  the  screenings  and  the  bleach  required  due  to  the  more 
even  cooking.  Frohberg 3  claims  that  the  rapidity  of  the  diges- 
tion, other  things  being  equal,  is  dependent  solely  on  the  con- 
centration of  the  free  S02  and  that  in  order  to  hasten  the  process 
dry  wood  and  liquor  rich  in  free  S02  should  be  used.  The 
present  tendency  is  toward  the  use  of  acid  of  high  strength,  par- 
ticularly in  free  SO2.  An  increase  in  this  factor  enables  the 
time  of  cooking  and  the  final  temperature  to  be  reduced.  The 
higher  test  for  the  digester  acid  means  a  higher  blowing  test  at 
the  end  of  the  cook  in  order  to  obtain  equal  yields.  It  used  to 
be  stated  that  the  best  acid  contained  75  per  cent  of  its  total 
S02  in  the  free  state  while  now  it  is  considered  that  80  to  85 
per  cent  is  a  better  figure.  Much  difference  of  opinion  exists 

1  Schlick:  Paper  Pulp  Mag.  Can.,  1915,  13,  227. 

2  Private  communication. 

3  Wochbl.  Papier-Fabr.,  1910,  41,  1179-1182 


PROGRESS   OF  THE  COOK  191 

regarding  the  relative  value  of  acids  of  different  compositions 
and  much  more  work  will  have  to  be  done  before  the  influence 
of  all  factors  can  be  definitely  established. 

In  the  cooking  process  irregularities  are  likely  to  occur  from 
very  obscure  causes.  Overcooking  may  be  caused  according  to 
Klason  1  if  too  little  lime  is  used.  The  minimum  amount  nec- 
essary to  saturate  the  lignosulphonic  acids  is  22.5  grams  per 
kilo  of  wood  and  if  less  than  this  amount  is  used  the  pulp  is 
overcooked  and  charred.  Overcooking  may  also  result  from 
decomposition  of  the  liquor  with  formation  of  free  sulphur 
according  to  the  reaction 

3  S02  =  2  S03  +  S. 

The  sulphur  acts  catalytically,  producing  further  decomposition 
of  the  calcium  bisulphite,  and  the  sulphuric  acid  combines  with 
the  lime  as  CaS04  so  that  not  enough  base  is  left  to  combine 
with  the  sulphonic  acids  which  polymerize  and  eventually  the 
fibre  is  attacked  and  darkened.  Selenium  in  the  cooking  liquor 
will  also  act  catalytically  and  with  far  greater  power  than  free 
sulphur.  Torgerson  and  Bay 2  have  proved  that  it  is  not  the 
selenium  directly  but  the  simultaneous  presence  of  dust  that 
causes  the  trouble.  This  dust  acts  as  an  energetic  contact  sub- 
stance promoting  catalytic  action  of  the  selenium.  This  action 
is  recognized  by  a  sudden  fall  in  the  S02  and  lime  contents  of 
the  liquor  after  the  digestion  has  proceeded  for  some  time. 
The  best  way  to  determine  the  progress  of  a  cook  is  to  titrate 

N 

portions  of  the  liquor  with  —  iodine  solution  which  will  show  the 

10 

amount  of  total  S02.  In  taking  samples  from  the  digester  for 
this  test  a  cooler  should  be  used,  otherwise  much  of  the  SO2 
will  be  lost.  Another  test  which  is  frequently  employed  is  to 
remove  samples  of  the  liquor  and  treat  them  with  a  mixture  of 
strong  ammonia  and  water  in  equal  parts  in  test  tubes.  This 

1  Klason:  Wochbl.  Papier-Fabr.,  1910,  41,  464  et  seq. 

2  Torgerson  and  Bay:  Papier-Fabr.,  1914,  12,  483. 


THE  SULPHITE  PROCESS 

causes  the  precipitation  of  calcium  monosulphite  which  is  at 
first  light  and  voluminous  but  which  decreases  in  quantity  as 
the  cooking  proceeds.  When  a  certain  volume  of  precipitate 
is  reached  the  cook  is  considered  finished.  This  test  is  usually 
stated  to  show  the  amount  of  lime  present  as  sulphite  but 
according  to  Oman  l  it  is  virtually  a  test  for  S02  since  if  enough 
of  the  latter  is  present  all  of  the  lime  will  be  precipitated.  By 
taking  the  sample  from  the  digester  through  a  cooler  and  adding 
some  calcium  chloride  to  the  ammonia  used  the  test  may  be 
made  to  indicate  the  amount  of  S02  present.  The  cooks  in 
charge  of  the  digesters  also  judge  of  the  condition  of  the  cook, 
to  a  certain  extent,  by  the  color  and  odor  of  samples  of  the 
liquor  removed  from  the  digester  at  frequent  intervals  toward 
the  end  of  the  cook. 

Recovery  of  Gas.  The  relief  of  gas  and  liquor  from  the 
digester  during  cooking  causes  a  very  large  loss  of  sulphur 
dioxide  and  the  recovery  of  this  is  an  important  item  in  keeping 
the  cost  for  sulphur  at  a  low  point.  This  is  accomplished  by 
passing  the  relief  through  separators  and  coolers  from  which 
the  gas  is  taken  to  the  acid  storage  tanks  where  it  is  absorbed 
and  brings  the  acid  to  the  desired  strength  for  cooking.  The 
liquid  portion  from  the  separator  is  either  allowed  to  go  to 
waste  or  is  mixed  with  the  acid  from  the  acid  system  previous 
to  strengthening  the  latter  with  relieved  gas.  In  Thome's2 
recovery  system  the  separated  and  cooled  gas  from  the  digester 
is  passed  into  the  bottom  of  a  tower  filled  with  wood  blocks 
over  which  the  acid  from  the  acid-  system  is  passed,  the  strength- 
ened acid  thus  formed  goes  to  the  storage  tanks.  The  liquor 
from  the  separator  contains  about  i  per  cent  of  S02  and  after 
cooling  it  is  sent  to  the  acid  system  with  the  water  or  milk  of 
lime  as  the  case  may  be.  This  system  is  equally  applicable 
to  the  limestone  or  milk  of  lime  systems  and  by  its  use  it  is  said 
to  be  possible  to  strengthen  an  acid  of  2.60  per  cent  total  and 
i  per  cent  combined  S02  up  to  5.50  per  cent  total  with  no  in- 

1  Oman:  Teknisk  Tidskrift,  1916,  46,  4. 

2  Thorne:  Pulp  Paper  Mag.  Can.,  1915,  p.  173  (March  15). 


BLOWING  AND   WASHING  193 

crease  in  the  amount  of  combined;  moreover  this  is  accomplished 
at  a  temperature  of  35°  C.  (95°  F.)  with  no  loss  of  gas. 

In  blowing  down  pressure  before  discharging  the  digester,  the 
gas  can  be  recovered  by  passing  the  gas  and  steam  under  the 
false  bottom  of  a  tower  in  which  there  is  a  continuous  shower 
of  water.  This  absorbs  the  gas  and  soon  becomes  heated  by 
the  steam  to  such  a  temperature  that  it  can  no  longer  hold  the 
gas  in  solution.  This  liberated  gas,  together  with  that  coming 
from  the  digester,  soon  increases  to  such  an  extent  that  the  water 
supplied  can  no  longer  absorb  it  and  there  is  delivered  from  the 
top  of  the  tower  a  constant  stream  of  pure  gas  which  can  be 
used  in  the  acid  system. 

In  a  few  instances  attempts  have  been  made  to  recover  the 
gas  liberated  when  the  digester  is  blown  into  the  blow  pits,  but 
the  volume  of  gas  and  steam  which  must  be  handled  in  a  very 
short  time  is  enormous  and  it  is  very  doubtful  if  the  results 
obtained  pay  for  the  expensive  equipment  and  the  cost  of  oper- 
ating. In  one  installation  where  this  is  being  tried  there  has 
been  no  reduction  in  the  amount  of  sulphur  used  per  ton,  indi- 
cating that  the  recovery  is  not  a  paying  proposition. 

The  sulphur  consumption  in  practical  work  is  generally  fig- 
ured from  the  weight  of  sulphur  fed  to  the  burners  and  the 
tons  of  pulp  produced.  Bryant 1  states  that  in  commercial 
work  the  sulphur  consumption  varies  from  235  to  400  Ibs.  per 
ton  and  that  the  amount  theoretically  necessary,  not  taking 
the  formation  of  sulphuric  acid  into  account,  would  be  184  Ibs. 
Schwalbe2  gives  the  sulphur  consumption  as  9  to  10  kgs.  per 
100  kgs.  fibre  (180  to  200  Ibs.  per  2000  Ibs.  fibre)  and  thinks  that 
it  should  be  possible  to  work  with  as  little  as  8  kgs.  (160  Ibs.  per 
ton).  Less  sulphur  per  ton  is  used  in  the  processes  where  in- 
direct steam  is  used  because  less  loss  is  incurred  by  dilution  and 
relieving  liquor. 

Blowing  and  Washing.  As  already  stated  the  contents  of  the 
digester  are  usually  discharged  into  the  blow  pit  under  a  pres- 

1  Bryant:  Paper,  Jan.  28,  1914. 

2  Schwalbe:  Chemie  der  Cellulose,  p.  530. 


IQ4  THE  SULPHITE  PROCESS 

sure  of  about  50  Ibs.  or  less.  The  pipe  from  the  digester  to  the 
blow  pit  may  be  of  copper  or  even  cast  iron  since  the  pitch  in 
the  pulp  covers  the  inside  of  the  pipe  and  prevents  corrosion. 
This  pipe  is  so  arranged  that  the  stock  is  discharged  against  a 
target  placed  in  one  end  of  the  blow  pit,  to  prevent  wear  on 
the  pit  walls.  This  target  may  be  of  bronze  or  of  hard  cast 
iron;  the  latter  is  generally  used  as  it  is  cheaper,  and  offers 
more  resistance  to  mechanical  wear  than  bronze.  As  the  acid 
at  this  stage  is  comparatively  weak  and  the  blowing  is  immedi- 
ately followed  by  washing  the  chemical  resistance  of  the  cast 
iron  is  sufficient  for  this  purpose. 

Blow  pits  are  of  various  shapes  but  consist  essentially  of 
tanks  with  false  bottoms  through  which  the  waste  liquor  may 
drain.  Modern  American  mills  often  use  perforated  tiles  in  .the 
pit  bottoms.  They  are  frequently  of  reenforced  concrete  lined 
with  wood  of  a  resinous  nature  such  as  Southern  pine  or  Doug- 
las fir.  The  washing  is  done  by  a  stream  of  water  from  a 
hose,  or  by  means  of  sprinkler  pipes,  and  requires  several  hours. 
A  novel  wash  pit  arrangement  is  that  proposed  by  Kuhn.1  The 
entire  floor  is  covered  with  drainer  tiles  and  the  wash  water 
enters  from  below  these  tiles  and  is  thoroughly  mixed  with  the 
stock  by  air  or  steam  forced  through  a  series  of  perforated 
pipes  laid  on  the  surface  of  the  tiles.  After  thorough  mixing 
in  this  way  the  wash  water  is  allowed  to  drain  off  by  opening 
the  appropriate  valves.  If  desired  this  process  can  be  repeated. 
The  claim  is  made  that  the  washing  of  15  tons  of  dry  fibre  can 
be  accomplished  in  37  minutes  as  follows:  15  minutes  for  filling 
with  hot  water,  15  minutes  for  washing  with  air  or  steam  and 
7  minutes  for  draining. 

The  treatment  of  the  pulp  after  washing  is  largely  a  mechani- 
cal one,  to  remove  dirt,  knots,  slivers,  and  uncooked  or  partly 
cooked  chips,  by  means  of  rifHers,  screens,  etc.  The  screenings 
thus  removed  amount  to  3  to  8  per  cent  of  the  pulp  produced. 
During  these  mechanical  purification  processes  the  stock  is  very 

1  Kuhn:  Papier-Fabr.,  1915,  13,  725  and  744. 


ROSIN  IN  PULP 


195 


largely  diluted;    one  authority  gives  the  concentration  of  the 
stock  as  follows: 

In  rifflers 250  parts  water  to  i  part  pulp 

In  coarse  screens 125  parts  water  to  i  part  pulp 

In  fine  screens 150  parts  water  to  i  part  pulp 

The  unbleached  sulphite  fibre  found  on  the  market  shows 
wide  variations  in  color,  strength  and  physical  properties.  Its 
chemical  composition  also  varies  more  or  less  as  is  proved  by 
the  following  table. 

ANALYSIS  OF  UNBLEACHED  SPRUCE  SULPHITE  FIBRE  * 


Mioisture   loss  at  100°  C 

Per  cent 
6.15 

Per  cent 
6  .70 

Per  cent 
6.57 

Per  cent 
6  .4$ 

Mineral  matter  (ash) 

I    .OO 

0.45 

o  .33 

/• 
0.65 

Hydrocellulose,  etc.,  soluble  in  alkali.  . 
Cellulose                                      

2-53 
8^.32 

2.26 

89.74 

4.25 

88.12 

1-52 
81.51 

Non-cellulose  (lignin)  by  difference.  .  .  . 

5.00 

0.85 

0-73 

9.87 

*  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  268. 

The  ash  in  sulphite  spruce  fibre  has  been  given  considerable 
study  by  Richter.1  He  finds  that  it  rarely  exceeds  i  per  cent 
and  is  usually  about  0.5  per  cent.  Silica,  generally  amounting 
to  about  one-third  of  the  total  ash,  is  probably  fixed  as  calcium 
or  magnesium  silicate  during  boiling  as  the  silica  present  in  the 
wood  is  too  little  to  account  for  so  much  in  the  fibre  ash.  The 
percentage  of  iron  in  the  ash  showed  no  constant  relationship  to 
the  total  ash  nor  to  any  characteristics  of  the  pulp. 

The  rosin  in  sulphite  has  been  given  much  attention  because 
of  its  possible  relation  to  rosin  spots  in  the  paper  made  from  it. 
Herzberg  gives  the  following  percentages  of  rosin  extracted  by 
ether : 


Bleached 

Unbleached 

Mitscherlich  pulp  

Per  cent 
o  .44 

Per  cent 
0.58 

Ritter-Kellner  pulp  

o  .43 

0.59 

Other    investigators    find    considerably    higher    amounts    as 
follows : 

1  Richter:  Wochbl.  Papier-Fabr.,  1913,  44,  1776. 


196 


THE  SULPHITE  PROCESS 


Ether  soluble 

Alcohol  soluble 

Total 

Foreign  sulphites  * 

Per  cent 
0.70-1.33 
0.65-1  .21 
0.82-0.98 
0.66-0.98 

Per  cent 
O.IO-O.22 
0.15-0.62 
0.18-0.82 
0.23-0.62 

Per  cent 
0.90-1.43 
0.86-1.52 
1.05-1.67 
I  .00-1  .60 

American  sulphites  *  .  . 

Unbleached  fibref.  .  . 

Bleached  fibre  f  

*  Richter:  Wochbl.  Papier-Fabr.,  1913,  44,  4507. 
t  Schwalbe:    Wochbl.  Papier-Fabr. ,  1913,  44,  3247. 

Both  Richter  1  and  Schwalbe 2  claim  that  the  ether  soluble 
portion  is  responsible  for  trouble  with  rosin  spots.  The  total 
material  contains  both  a  fatty  and  a  resinous  constituent  and 
Schwalbe  has  shown  experimentally  that  neither  constituent 
alone  will  produce  rosin  spots  but  that  both  together  will  give 
distinct  and  characteristic  spots.  The  best  means  of  avoiding 
rosin  troubles  seems  to  be  seasoning  the  wood,  which  reduces 
the  rosin  soluble  in  ether  and  alcohol.  Changes  in  the  char- 
acter of  the  rosin  extracted  from  the  wood  indicate  that  storage 
of  chips  for  two  to  three  weeks  in  the  open  air  is  as  effective 
as  storing  the  logs  for  two  years.  Richter  3  gives  the  following 
figures  for  rosin  in  cellulose  from  the  same  wood  wet  and  dry. 


Rosin  in  cellulose 


Moisture  in  wood 

Ether  soluble 

Alcohol  soluble 

Total 

Per  cent 
49.0 

Per  cent 
1  .00 

Per  cent 

O.II 

Per  cent 
1  .11 

0-5 

0.38 

0.26 

0.64 

35-0 

I-3I 

0.31 

1.62 

5-o 

0.88 

0.36 

1.24 

Bleaching  largely  eliminates  rosin  troubles  and  with  well- 
bleached  pulp  trouble  from  this  source  is  seldom  encountered. 

For  the  demonstration  of  rosin  in  sulphite  fibre,  Klemm 4  uses 
a  strong  solution  of  Sudan  III  in  a  mixture  of  three  parts  alcohol 

1  Richter:  Wochbl.  Papier-Fabr.,  1913,  44,  2486. 

2  Schwalbe:  Wochbl.  Papier-Fabr.,  1914,45,  2926. 

3  Richter:  Wochbl.  Papier-Fabr.,  1913,  44,  4621. 

4  Klemm:  Wochbl.  Papier-Fabr.,  1911,  42,  967. 


MODIFIED   SULPHITE  PROCESSES  197 

and  one  part  water.  The  sample  is  reduced  to  a  pulp  with 
water,  drained  and  the  moist  fibres  treated  with  the  dye.  The 
excess  is  removed  by  blotting  paper  and  the  fibres  mounted  for 
observation  in  water.  The  rosin  will  be  found  stained  orange 
red  while  the  fibre  is  uncolored. 

Modified  Sulphite  Processes.  Numerous  modifications  of 
the  sulphite  process  have  been  tried  out  and  patented  from  time 
to  time.  It  would  be  impossible  to  enumerate  all  of  these  but 
a  few  may  be  mentioned  as  showing  the  trend  of  modern  investi- 
gations. 

Eichmann  *  first  subjects  the  wood  to  the  action  of  gaseous 
862  and  then  boils  with  sulphite  liquor  as  usual. 

Moore  and  Wolf 2  charge  the  digester  with  chips  and  liquor  as 
usual,  close  the  head  and  then  inject  gaseous  S02,  air  being 
allowed  to  escape.  The  charge  is  allowed  to  stand  without  heat- 
ing to  allow  the  SO2  to  penetrate  and  steam  is  then  passed  in 
until  the  cook  is  complete.  The  injection  of  SO2  gas  is 
repeated  during  the  steaming  to  make  up  for  the  dilution  by 
condensation. 

Morterud 3  takes  the  liquor  from  under  a  false  bottom  in  the 
digester,  passes  it  through  a  heater  and  back  into  the  top  of  the 
digester,  thus  maintaining  good  circulation  and  cooking  with 
weaker  liquors  because  there  is  no  subsequent  dilution  by  con- 
densation. This  process  is  giving  excellent  satisfaction  in  the 
sulphate  pulp  industry  and  is  claimed  to  be  equally  applicable  to 
the  sulphite  process. 

Sammet  and  Merrill 4  have  obtained  a  United  States  patent  for 
cooking  with  gaseous  ammonia,  sulphur  dioxide  and  steam  instead 
of  the  usual  liquor.  Somewhat  similar  is  the  process  of  Tyborow- 
ski 5  who  causes  ammonia  to  react  with  sulphite  liquor,  thus 
precipitating  calcium  monosulphite,  which  is  removed,  and 

1  German  Patent  184,991,  May  31,  1906. 

2  U.  S.  Patent  1,119,977,  Dec.  8,  1914. 

3  German  Patent:  286,074,  Class  55)3,  Dec.  28,  1913. 

4  Paper  Trade  J.,  March  14,  1912,  p.  46. 
6  U.  S.  Patent  621,692,  June  16,  1914. 


198  THE  SULPHITE  PROCESS 

obtaining  a  cooking  liquor  containing  ammonium  sulphite  and 
free  ammonia. 

The  claims  for  nearly  all  of  these  modified  processes  are  much 
alike,  viz.:  shorter  time,  lower  temperature,  lighter  colored, 
stronger  and  easier  bleaching  fibre,  greater  yield,  etc. 

By-products  and  Waste  Liquor.  The  sulphite  process  offers 
opportunities  for  the  recovery  of  by-products  which  are  now  lost 
during  the  period  of  relieving  or  in  the  waste  liquor.  Bergstrom  l 
states  that  the  vapors  condensed  from  the  digesters  yield  an 
aqueous  distillate  containing  methyl  alcohol,  acetone,  aldehyde 
and  traces  of  acetic  and  formic  acids  together  with  a  brown  oil 
floating  on  the  surface.  This  oil  contains  7  per  cent  boiling 
between  150°  and  160°  C.,  55  per  cent  boiling  from  160°  to  190°  C. 
and  17  per  cent  boiling  between  190°  and  210°  C.  The  portion 
boiling  between  160°  and  190°  C.  consists  largely  of  cymene. 
The  specific  gravity  of  the  various  fractions  varies  from  0.845  to 
0.951.  The  same  author2  states  that  in  the  Ritter-Kellner 
process  8  to  10  kgs.  of  methyl  alcohol  are  formed  per  ton  of  easy 
bleaching  cellulose  produced;  of  this  about  3  kgs.  may  be  obtained 
from  the  relieved  gases.  If  the  waste  lyes  are  distilled  in  a 
continuous  column  apparatus  the  distillate  contains  methyl 
alcohol,  acetaldehyde,  acetone,  oils  and  SC>2  as  well  as  small 
quantities  of  formic  and  acetic  acids. 

The  problem  presented  by  the  waste  liquors  of  the  sulphite 
prpcess  is  one  which  is  not  only  interesting  from  a  chemical 
standpoint  but  has  also  attracted  much  attention  because  of  its 
bearing  on  stream  pollution.  In  some  cases,  particularly  in 
Europe,  mills  have  even  been  obliged  to  close  because  it  has  been 
found  impossible  to  purify  the  waste  liquors  sufficiently  to  com- 
ply with  the  legal  requirements.  While  the  industry  in  the 
United  States  is  not  confronted  with  quite  such  serious  con- 
ditions it  is  only  a  question  of  time  before  much  more  complete 
purification  will  be  demanded,  so  that  the  desirability  of  an  early 

1  Bergstrom:  Papier-Fabr.,  1912,  10,  359. 

2  Bergstrom:  Papier-Fabr.,  1912,  10,  677. 


WASTE  LIQUOR  199 

solution  is  very  evident.  The  present  method  of  purification,  if 
it  may  be  called  such,  is  merely  to  separate  the  fibres  and  neutral- 
ize the  free  acid  with  lime.  The  material  thus  removed  is  com- 
paratively small  in  amount  considering  that  for  every  ton  of 
fibre  produced  there  is  a  ton  of  organic  matter  dissolved  in  the 
waste  liquor.  The  total  amount  of  this  waste  in  the  United 
States  was  estimated  by  the  Geological  Survey  to  be  a  billion 
pounds  annually  as  long  ago  as  1913.  The  discharge  of  such 
vast  quantities  of  waste  into  streams  renders  the  water  injurious, 
to  health  and  makes  it  unfit  for  boiler  use.  It  aids  in  the  develop- 
ment of  algae  which  may  even  grow  in  such  quantities  as  to  cjioke 
the  streams.  Under  certain  conditions  it  may  cause  the  develop- 
ment of  hydrogen  sulphide  with  accompanying  loss  of  oxygen  in 
the  water  and  consequent  death  of  animal  and  vegetable  life. 

Considerations  of  the  nature  outlined  above  as  well  as  the 
desire  to  obtain  useful  and  valuable  products  from  a  waste  of 
such  enormous  magnitude  have  led  many  investigators  to  take 
hold  of  the  problem.  Walker  l  describes  the  waste  liquor  as  a 
dark,  reddish  brown  fluid  of  a  specific  gravity  of  about  1.05,  and 
having  a  peculiar,  not  unpleasant  odor.  Among  the  constitu- 
ents present  he  mentions  sulphur  dioxide,  sulphur  trioxide, 
free  sulphur,  calcium  and  magnesium  lignin  sulphonates,  pentoses 
and  pentosans,  mannose,  dextrose,  galactose,  free  furfural,  traces 
of  vanillin  or  vanillin-like  body  and  small  quantities  of  terpene- 
like  substances.  Waste  liquors  obtained  in  cooking  hemlock 
wood  have  the  following  composition,  according  to  Bryant : 2 


Grams  per  liter 

Pounds  per  ton  of  pulp 

Total  solids  

115  .00 

2999 

Loss  on  ignition 

IOZ   36 

2748 

Ash 

Q   64 

251 

Total  sulphur                        

7.83 

204 

Sulphur  as  SOs  

0.76 

20 

The  specific  gravity  of  this  liquor  was  1.0425. 

1  Walker:  J.  Soc.  Chem.  Ind.,  32  (1913),  389. 

2  Bryant:  Paper,  1914,  Jan.  28. 


200 


THE  SULPHITE  PROCESSS 


Klason  1  calculates  that  for  every  ton  (2202  Ibs.)  of  dry  fibre 
produced  the  waste  liquor  contains  the  following: 

600  kgs.  (1320  Ibs.)  lignin. 

200  kgs.  (441  Ibs.)  sulphur  dioxide  combined  with  lignin. 

90  kgs.  (198  Ibs.)  CaO  combined  with  lignin  sulphonic  acid. 
325  kgs.  (717  Ibs.)  carbohydrates. 

i5  kgs.  (33  Ibs.)  proteins. 

30  kgs.  (66  Ibs.)  rosin  and  fat. 

According  to  Krause 2  the  principal  constituent  in  the  waste 
liquor  is  the  calcium  salt  of  lignin-sulphonic  acid.  Ritter-Kellner 
liquor  is  darker  and  contains  more  furfural  and  generally  more 
sugars  than  Mitscherlich  liquor.  Wood  boiled  in  the  autumn 
contained  about  twice  as  much  sugar  as  wood  obtained  in  the 
spring.  Very  careful  analyses  of  liquor  from  autumn  cut  wood 
gave  the  following  figures: 


Mitscherlich  process 

Ritter-Kellner 
process 

Furfural                   

Per  cent 

O.OI 

Per  cent 

O.O2 

Pentosans  

0.40 

O  .20 

Hexosans  

O.2I 

0.40 

Total  sugars  

1.48 

I  .47 

Pentoses  

0.47 

o  .41 

Mannose  

0.48 

0.48 

Levulose  

0.28 

O.25 

Galactose  

O.OI 

O.OI 

Dextrose 

Trace 

According  to  Johnsen  3  the  volume  of  liquor  which  can  be 
obtained  without  special  apparatus  is  740  to  800  gallons  per  ton  of 
pulp,  while  Haegglund4  claims  to  obtain  960  gallons.  Great 
differences  of  opinion  also  exist  as  to  the  rate  of  formation  of 
fermentable  sugar  during  the  cook.  Krieble  5  states  that  most  of 
the  sugar  is  formed  before  the  end  of  the  seventh  hour  and  that 

1  Klason:  Papier-Fabr.,  1909,  26,  627,  671,  703. 

2  Krause:  Chem.  Ind.,  1906,  29,  217. 

3  Johnsen:  Pulp  Paper  Mag.  Can.,  16,  1918,  314. 

4  Haegglund:  Pulp  Paper  Mag.  Can.,  15,  1917,  1185. 

5  Krieble:  Paper,  23,  1919,  753. 


WASTE  LIQUOR  2OI 

part  of  the  fermentable  material  is  destroyed  if  the  temperature 
rises  above  145°  C.  after  that  time.  Haegglund,  on  the  other 
hand,  claims  that  only  a  little  sugar  is  formed  during  the  first  six 
or  eight  hours  but  that  it  increases  rapidly  on  longer  cooking, 
the  rate  depending  on  temperature  and  composition  of  the  cooking 
acid. 

Hoenig x  claims  that  no  organic  acids  except  formic  and  acetic 
are  present  and  that  the  ratio  of  these  is  i  :  1.56.  He  finds  2.15 
to  9.08  grams  of  volatile  acid  per  liter. 

The  waste  liquor,  according  to  Walker,2  yields  brominated  and 
chlorinated  products;  it  contains  active  carbonyl  and  methyl 
groups  and  is  a  strong  reducing  agent.  On  addition  of  alcohol 
the  chief  constituents  are  precipitated  as  a  dark,  gummy  mass 
which  becomes  brittle  on  drying.  This  may  also  be  obtained  by 
salting  out  with  sodium  chloride  or  by  treating  with  concentrated 
mineral  acids  or  lead  acetate.  It  is  almost  impossible  to  purify 
this  substance  because  of  its  colloidal  nature  and  its  limited 
solubility  in  the  usual  organic  solvents. 

The  attempts  to  utilize  the  materials  in  this  waste  liquor  have 
been  very  numerous  and  many  patents  have  been  issued  covering 
all  kinds  of  industries.  A  complete  enumeration  of  all  the 
patents  in  detail  would  occupy  too  much  space  and  moreover  it 
has  been  well  covered  by  Miiller3  up  to  the  year  1911  and  also 
by  Johnsen  and  Hovey.4  A  brief  outline  of  the  more  important 
uses,  or  proposed  uses,  is  therefore  all  that  will  be  attempted  here. 

As  a  binder  the  waste  liquor,  either  in  its  original  strength  or 
concentrated  by  evaporation,  has  been  tried  for  various  purposes. 
As  a  road  binder  liquor  at  1.13  sp.  gr.  has  given  very  fair  service 
when  sprinkled  upon  the  streets.  While  it  is  not  water-resistant, 
the  roads  to  which  it  has  been  applied  appear  to  resist  the  action 
of  rains  fully  as  well  as  those  to  which  crude  oil  has  been  applied. 
This  use  has  only  local  interest  because  of  the  cost  of  transporting 

1  Hoenig:  Chem.  Ztg.,  1912,  36,  889. 

2  Walker:  J.  Soc.  Chem.  Ind.,  32  (1913),  389. 

3  Miiller:  Literatur  der  Sulfit-Ablauge. 

4  Bulletin  66,  Dept.  of  Interior,  Canada,  1919. 


2O2 


THE  SULPHITE  PROCESS 


the  relatively  dilute  liquors.  In  preparing  briquettes  from 
waste  coal  it  has  met  with  some  success,  the  briquettes  being 
hard  and  making  excellent  fuel  in  ordinary  grates  or  in  smelting 
furnaces.  An  advantage  which  it  possesses  for  this  work  is  that 
the  briquettes  do  not  soften  on  heating  and  hence  hold  their 
shape  well  in  use.  On  the  other  hand,  the  high  percentages  of 
ash  and  sulphur  are  detrimental  in  some  cases.  The  briquetting 
of  pyrites,  wood  waste,  iron  ores  and  other  materials  has  also 
been  successfully  carried  out  by  means  of  the  concentrated  waste 
liquor.  Another  use  as  a  binder  is  in  the  iron  foundry  where 
it  is  mixed  with  the  sand  in  preparing  the  moulds.  Stutzer 1 
gives  the  following  as  the  composition  of  a  sulphite  waste  liquor 
and  two  concentrated  products  made  therefrom: 


Original  waste 
liquor 

Wood  extract 

Cell  pitch 

Dry  matter  
Ash  constituents  

12.  18 
I  .44 

63.88 
2    64 

82.79 
IA.  QO 

Lime 

o  87 

O    ZO 

8  =:o 

Total  sulphur 

o  8<? 

4  80 

1  87 

SO2 

o  24 

O    I1? 

o  8< 

In  the  preparation  of  concentrated  products  either  iron  or 
copper  apparatus  may  be  used,  but  if  the  former  is  employed  the 
acid  in  the  liquor  must  be  neutralized  by  lime.  Direct  evapora- 
tion in  copper  is  preferable  if  the  product  is  to  be  used  in  tanning. 
A  multiple  effect  evaporator  is  generally  employed  to  bring  the 
liquor  to  35°  Be.  and  the  final  concentration  is  performed  on 
drums  one  of  which  will  bring  it  up  to  60°  Be.  while  a  second  will 
convert  it  to  a  solid.  The  pitch  appears  as  a  black  opaque  resin 
but  is  soluble  in  water.  About  i  kg.  of  dry  pitch  is  obtained 
from  10  kgs.  of  waste  liquor  and  for  each  ton  produced  about  a 
ton  of  coal  is  required. 

It  has  been  proposed  by  Knosel 2  to  prepare  a  fertilizer  from 
the  waste  liquor  by  evaporating  to  about  25°  Be.  and  mixing  with 

1  Stutzer:  Papier  Ztg.,  1911,  36,  5. 

2  Knosel:  German  Pat.  128,213. 


USES   FOR  WASTE  LIQUOR  203 

about  an  equal  weight  of  ground  Thomas  slag.  Analyses  of  this 
product  show  that  practically  all  the  phosphoric  acid  is  in  the 
citrate  soluble  form. 

The  use  of  sulphite  waste  liquor  in  the  sizing  of  paper  has  been 
proposed  by  Mitscherlich  l  who  mixed  the  liquor  with  gelatin 
solution  and  separated  the  precipitate  formed.  This  was  then 
dissolved  in  weak  alkali  and  added  to  the  paper  stock  in  which 
it  was  precipitated  by  alum.  A  sizing  process  of  another  kind 
is  that  of  Klason  2  in  which  the  waste  liquor  is  used  instead  of 
alum  as  a  precipitant  for  silicate  of  soda.  Neither  of  these 
processes  has  ever  come  into  extensive  use. 

Stutzer 3  has  investigated  the  possibilities  of  waste  liquor  in 
the  preparation  of  cattle  feed  and  asserts  that  in  each  kilo,  con- 
taining 120  grams  per  liter  of  solids,  there  are  550  calories  which 
can  be  made  available  by  feeding.  His  proposed  treatment  is  to 
evaporate  100  liters  to  50  liters  in  a  vacuum,  mix  with  0.5  kg. 
of  formaldehyde  and  ground  limestone  and  then  filter.  The 
filtrate,  after  further  evaporation,  is  mixed  with  molasses  and 
6.25  kgs.  of  peat  to  give  45  kgs.  of  cattle  food. 

In  the  dyestuff  industry  it  has  been  used  as  the  basis  for  the 
manufacture  of  sulphur  dyes,  in  the  reduction  of  indigo  and  in 
the  preparation  of  indanthrene  and  similar  dyes.  The  sodium 
lignin  sulphonate  prepared  from  it  has  been  employed  to  replace 
tartaric  acid  in  mordanting  wool. 

Strehlenert 4  has  proposed  the  following  method  for  the  prepa- 
ration of  lignin  and  the  recovery  of  sulphur  dioxide.  A  little 
acid  sodium  sulphate  is  added  to  the  fresh  hot  liquor  and  the 
calcium  sulphate  which  precipitates  is  separated.  The  hot  liquor 
is  then  run  into  digesters  and  heated  to  100°  C. ;  air  is  pumped  in 
until  the  pressure  reaches  18  atmospheres,  when  the  temper- 
ature rises  20°  because  of  the  chemical  reactions  taking  place. 
Heating  is  continued  to  160°  C.  Between  160°  and  170°  C.  is 

1  Mitscherlich:  German  Pat.  54,206,  1890. 

2  Klason:  Z.  angew.  Chem.,  22  (1909),  1423... 

3  Stutzer:  Z.  angew.  Chem.,  22  (1909),  1999. 

4  Strehlenert:  Papier-Fabr.,  1913,  n,  645,  666. 


204  THE  SULPHITE  PROCESS 

the  critical  point  at  which  decomposition  of  the  lignin  sulphonic 
acid  begins.  This  reaction  causes  the  temperature  to  rise  about 
20°  more  and  it  is  finally  forced  up  to  200°  C.  The  time  after 
reaching  100°  C.  is  about  40  to  60  minutes.  If  properly  con- 
ducted this  procedure  causes  the  evolution  of  sulphur  dioxide, 
which  can  be  recovered,  while  the  lignin  is  precipitated  in 
granular  form  and  can  be  used  as  fuel  after  partial  drying.  The 
sulphur  recovery  is  claimed  to  be  25  to  30  kgs.  (55  to  66  Ibs.)  per 
ton  of  pulp  and  the  lignin  enough  to  supply  the  entire  fuel 
requirements  of  the  pulp  mill. 

The  use  of  the  dried  waste  liquor  as  a  fuel  is  suggested  be- 
cause of  the  large  amount  of  combustible  matter  which  it  con- 
tains. The  dry  material  is  light,  powdery  and  has  a  heating 
value  of  about  6000  B.t.u.  per  pound.  Experiments  in  burn- 
ing this  in  the  same  manner  as  powdered  coal 1  gave  excellent 
results  and  the  ash  formed  in  easily  accessible  places  and  showed 
no  tendency  to  fuse. 

Rinman 2  mixes  the  waste  liquor  with  lime  to  make  22  to  25 
grams  per  liter  of  calcium  oxide  and  boils  first  for  five  hours  at  a 
low  temperature  and  finally  at  180°  C.  The  precipitate  of  cal- 
cium sulphite  and  humus  is  filtered  off  and  treated  with  sulphur 
dioxide  to  recover  the  calcium  bisulphite.  The  alkaline  filtrate 
is  evaporated  to  40°  Be.,  more  lime  is  added,  the  mass  evapo- 
rated to  dryness  and  finally  destructively  distilled  in  presence 
of  steam.  The  products  of  this  latter  process  include  acetone 
and  low  and  high  boiling  oils. 

The  preparation  of  a  material  for  use  in  making  insulating 
substances  or  artificial  leather  is  patented  by  Trainer.3  The 
waste  liquor  is  evaporated  to  30°  Be.  and  then  heated  with  an 
acid,  preferably  after  adding  an  aldehyde  such  as  formaldehyde. 

Extracts  for  use  in  tanning  leather  are  prepared  in  consider- 
able quantities  by  processes  involving  neutralization  with  lime, 
concentration,  and  subsequent  separation  of  the  organic  and 

1  Paper,  Dec.  19,  1917. 

2  Papier  Ztg.,  Apr.  4,  1915. 

3  Trainer:  German  Pat.  i97,i95>  Feb.  20> 


USES   FOR  WASTE  LIQUOR  205 

inorganic  materials.  The  extracts  obtained  contain  practically 
no  true  tannins  but  do  contain  materials  which  are  taken  up  by 
the  skins  and  act  as  fillers.  While  these  extracts  are  not  suit- 
able for  tanning  alone  they  find  a  legitimate  use  as  additions 
to  other  true  tanning  substances. 

The  preparation  of  alcohol *•  from  waste  lyes  has  probably 
attracted  more  attention  than  .any  other  method  of  utilization 
and  a  number  of  commercial  plants  are  already  in  successful 
operation.  The  two  principal  processes  now  in  use  are  the 
Swedish,  which  is  a  combination  of  the  Wallin  and  Ekstrom  proc- 
esses, and  the  Norwegian  or  Landmark  method.  The  principle 
of  all  processes  is  the  fermentation  of  the  sugars  present  followed 
by  the  distillation  of  the  alcohol  formed,  and  one  of  the  prin- 
cipal difficulties  encountered  has  been  due  to  the  poisoning  of 
the  yeast  by  traces  of  sulphur  dioxide.  The  Swedish  process 
uses  a  tempered  yeast  which  is  capable  of  resisting  this  action. 
The  liquor  is  first  neutralized  by  calcium  carbonate  and  the 
last  traces  of  acidity  by  calcium  hydroxide,  it  is  then  cooled, 
settled  and  run  to  the  fermentation  vats  where  the  yeast  is 
added.  It  is  fermented  at  27°  C.  for  four  or  five  days  and  then 
distilled.  The  raw  alcohol  contains  92  to  93  per  cent  of  ethyl 
alcohol,  3  to  4  per  cent  methyl  alcohol  and  small  amounts  of 
cymol,  acetone  and  aldehyde.  The  yield  of  100  per  cent  alcohol 
by  this  process  is  said  to  be  74  liters  per  ton  of  dry  sulphite, 
and  the  cost  about  12  cents  per  U.  S.  gallon  180  proof. 

In  the  Norwegian  process  the  fermentation  is  aided  by  a 
nutrient  and  easily  fermentable  medium  prepared  from  milk 
or  whey.  To  the  milk  an  equal  volume  of  sulphite  liquor  is 
added  and  a  small  amount  of  muriatic  acid  and  the  precipitated 
ligno-casein  filtered  off.  The  filtrate  is  then  added  to  the  waste 
liquor  and  the  mixture  evaporated  to  a  concentration  of  about 
15  per  cent.  It  is  next  neutralized  by  powdered  limestone, 
cooled  to  27°  C.  and  the  yeast  added;  in  this  case  ordinary 

1  Tartar:  J.  Ind.  and  Eng.  Chem.,  1916,  226;  Hedalen:  Pulp  Paper  Mag. 
Can.,  1916,  176;  Kiby:  Chem.  Ztg.,  1915,  39,  212  et  seq.;  Segerfelt:  Papier.  Ztg., 
53,  2518,  2558. 


206  THE  SULPHITE   PROCESS 

brewers'  yeast  has  proved  entirely  satisfactory.  After  four  or 
five  days'  fermentation  it  is  ready  to  be  distilled.  The  yield  by 
this  process  is  claimed  to  be  91.2  liters  of  100  per  cent  alcohol 
per  ton  of  dry  sulphite,  and  the  cost  about  9  cents  per  U.  S. 
gallon  1 80  proof. 

According  to  McKee  1  the  so-called  poisoning  of  the  yeast 
is  not  due  to  sulphur  dioxide  but  to  the  lack  of  oxygen.  He 
has  patented  a  process  in  which  the  hot  waste  liquor  is  cooled 
by  blowing  air  through  it  and  then  placed  in  closed  fermenta- 
tion tanks  where  it  is  kept  agitated  during  the  fermentation 
period  by  a  slow  current  of  air.  Under  these  conditions  fer- 
mentation proceeds  satisfactorily  with  ordinary  yeast  even  in 
the  presence  of  very  considerable  amounts  of  sulphur  dioxide. 
Loss  of  alcohol  is  prevented  by  scrubbing  the  exit  gases  from 
the  fermentation  tanks  with  unfermented  liquor. 

According  to  Stalnacke 2  three  mills  in  Sweden  were  produc- 
ing in  1916  about  660,000  gals,  of  100  per  cent  alcohol  annually, 
while  the  total  possible  production  was  about  6,868,000  gals. 
Considering  the  equipment  necessary  he  states  that  for  a  mill 
making  55  tons  of  cellulose  the  fermentation  vats  should  hold 
264,000  gals,  and  the  distilling  apparatus  should  be  capable  of 
handling  about  2400  gals,  per  hour. 

While  the  preparation  of  alcohol  from  the  waste  liquor  is  a 
profitable  undertaking  it  does  not  solve  the  problem  of  the  dis- 
posal of  the  liquor  since  the  spent  fermentation  residues  are 
nearly  as  objectionable  as  the  original  waste. 

Other  substances  which  it  has  been  proposed  to  recover  from 
the  waste  liquor  are  antiseptic  materials,  calcium  sulphite,  cal- 
cium sulphate,  coniferin,  cymol,  acetic  acid,  furfural,  levulinic 
acid,  oxalic  acid,  sulphur,  turpentine,  lignorosin,  vanillin,  etc. 
Many  of  these  can  be  obtained  only  in  small  amounts  and  the 
demand  and  the  prices  obtainable  are  not  such  as  to  make  the 
undertaking  attractive. 

1  McKee:  Paper  Trade  J.,  1918,  Aug.  22,  p.  42. 

2  Stalnacke:  Paper,  Apr.  5,  1916. 


TESTS  AND   ANALYSES  207 

While  much  progress  has  been  made  there  is  still  a  tremen- 
dous amount  of  work  to  be  done  before  the  utilization  of  this 
enormous  amount  of  waste  can  be  considered  satisfactory.  The 
quantity  of  material  to  be  handled  would  seem  to  indicate  that 
such  investigations  should  be  directed  towards  the  production 
of  large  amounts  of  products  at  small  profits  rather  than  the 
preparation  of  small  quantities  of  substances  of  relatively  high 
value  per  pound. 

Tests  and  Analyses  for  the  Sulphite  Process  —  Sulphur. 
Sulphur  as  obtained  at  present  on  the  American  market  is  of  a 
very  high  degree  of  purity  but  it  is  nevertheless  well  to  examine 
it  occasionally. 

Moisture  may  be  determined  by  weighing  a  3  to  5  gram  por- 
tion into  a  weighing  bottle,  drying  to  constant  weight  at  70°  to 
80°  C.,  cooling  and  again  weighing.  The  heating  should  not 
be  prolonged  beyond  the  time  necessary  to  reach  constant 
weight  and  the  temperature  must  not  be  allowed  to  rise  too 
high. 

To  determine  non- volatile  substances  a  10  gram  sample  is 
cautiously  heated  in  a  porcelain  crucible  on  a  sand  bath  until 
nearly  all  of  the  sulphur  has  volatilized  (ignition  of  the  sulphur 
must  not  take  place).  Cover  the  crucible  with  a  perforated 
lid  and  pass  into  it  pure,  dry  hydrogen  gas  until  all  sulphur 
has  escaped;  cool  and  weigh  as  non- volatile  matter. 

The  inorganic  ash  may  be  determined  by  igniting  the  non- 
volatile matter  with  access  of  air  and  reweighing  after  cooling. 

Selenium  may  be  determined  according  to  the  method  of 
W.  Smith l  as  follows :  Weigh  30  to  50  grams  of  the  finely 
ground  sulphur  into  an  Erlenmeyer  flask,  add  a  few  cubic  centi- 
meters more  bromine  than  the  grams  of  sulphur  used  and  allow 
it  to  stand  15  minutes.  Transfer  to  a  100  c.c.  separatory  funnel 
and  shake  vigorously  with  40  c.c.  of  bromine  water  for  one 
minute.  Separate  the  sulphur  bromide  from  the  aqueous  solu- 
tion and  pour  the  latter  through  a  wetted  filter  paper.  Add 

1  W.  Smith:  J.  Ind.  Eng.  Chem.,  1915,  7,  849. 


208  THE   SULPHITE   PROCESS 

about  2  c.c.  of  bromine  and  40  c.c.  of  bromine  water  to  the 
sulphur  bromide,  and  repeat  the  extraction  four  times,  keeping 
the  last  extract  separate.  Treat  the  last  extract  in  the  same 
way  as  the  combined  extracts,  using  proportionate  parts  of 
potassium  iodide  and  hydrochloric  acid  and  if  the  presence  of 
selenium  is  proved  repeat  the  extraction  as  often  as  necessary. 
The  combined  extracts  are  boiled  till  clear  and  any  remaining 
free  bromine  is  removed  by  careful  additions  of  powdered 
potassium  metabisulphite  or  sulphite  until  the  solution  just 
becomes  colorless.  Dilute  to  about  250  c.c.,  add  15  c.c.  of 
hydrochloric  acid  and  about  5  grams  of  potassium  > iodide  and 
boil;  this  completes  the  precipitation  of  the  selenium,  and 
gradually  converts  the  red  to  the  black  form.  The  free  iodine 
is  removed  by  a  few  cubic  centimeters  of  potassium  sulphite 
solution;  the  solution  is  boiled  for  20  minutes,  filtered  through 
a  tared  Gooch  crucible,  the  selenium  washed  with  hot  water, 
and  dried  at  100°  C.  until  constant  in  weight. 

Burner  Gases.  In  order  to  control  the  burners  properly  the 
gases  should  be  tested  once  an  hour,  or  oftener  if  the  burners 
are  not  working  satisfactorily.  The  sulphur  dioxide  may  be 
determined  by  means  of  an  Orsat  apparatus  using  caustic  soda 
in  the  absorption  pipette.  The  gas  is  measured  in  the  burette 
over  water  which  soon  becomes  saturated  with  SOz  and  then 
introduces  only  a  very  slight  error. 

Excess  air  may  be  estimated  by  determining  the  oxygen  by 
means  of  alkaline  pyrogallate  after  first  absorbing  the  SOz  in 
caustic  soda.  This  test  gives  valuable  information  regarding 
leaks  in  the  apparatus  between  the  combustion  chamber  and 
the  absorption  system. 

Sulphur  trioxide  in  the  gases  is  very  difficult  to  determine 
with  accuracy.  Richter  1  passes  the  gas,  at  a  rate  of  1000  c.c. 
in  20  to  25  minutes,  first  through  a  hard  glass  sampling  tube 
surrounded  with  an  iron  jacket  and  then  through  a  tube  30  cms. 
long  which  is  filled  with  garnets  and  bits  of  porcelain  and  cooled 

1  Papier-Fabr.,  u,  1913,  p.  610. 


TESTS  AND   ANALYSIS  '209 

with  ice.  The  gas  is  measured  by  the  amount  of. water  de- 
livered by  the  syphon  bottle  which  is  used  to  induce  its  flow. 
After  passing  2  to  5  liters  of  gas  the  tube  is  washed  out  by 
drawing  pure  air  through  it  and  finally  is  washed  into  a  beaker 
with  water  to  remove  the  SO3.  This  is  then  determined  gravi- 
metrically  by  precipitation  as  BaSCX 

The  generally  accepted  place  to  sample  the  gases  is  in  the 
main  pipe  between  the  cooler  and  the  absorption  apparatus. 

Besides  these  chemical  tests  it  is  customary  to  record  the 
temperature  of  the  gases  as  they  leave  the  combustion  chamber 
and  again  after  passing  the  cooler.  Some  form  of  recording 
pyrometer  is  desirable  for  the  former  work  while  an  ordinary 
chemical  thermometer  is  satisfactory  for  the  latter. 

"Acid"  or  Bisulphite  Liquor.  Samples  of  the  liquor  delivered 
by  the  absorption  apparatus  are  generally  tested  once  an  hour 
and  the  liquor  in  the  storage  tanks  whenever  a  digester  is  filled. 

For  total  SOz  a  i  c.c.  sample  is  taken  by  means  of  a  pipette 
and  diluted  with  200  to  300  c.c.  of  water  in  a  white  porcelain 

N 

bowl.     A  few  drops  of  starch  solution  are  added  and  then  — 

10 

iodine  solution  is  run  in  until  a  blue  color  appears. 

N 

For  free,  or  available,  SO2  a  i  c.c.  sample  is  titrated  with  — 

10 

caustic  soda,  using  phenolphthalein  as  an  indicator. 

The  combined  SO2  is  the  difference  between  the  total  and 
free  SO2. 

The  tests  given  are  those  generally  made  by  the  mill  foremen 
and  are  intended  to  give  comparative  rather  than  absolute 
results.  They  are  subject  to  errors  because  of  the  small  size  of 
the  sample,  and  because  the  pipette  is  not  usually  washed  out 
and  hence  a  little  of  the  liquor  always  remains  adhering  to  the 
glass.  It  is  customary  to  read  from  a  chart  the  amount  of 
either  free  or  total  SO2  corresponding  to  the  volume  of  caustic 
soda  or  iodine  used.  This  is  generally  spoken  of  as  per  cent,  but 
it  is  not  exactly  that  as  the  test  made  in  this  way  takes  no 
account  of  the  specific  gravity  of  the  liquor. 


' 


2IO  THE   SULPHITE  PROCESS 

For  accurate  analyses  of  the  liquor  a  sample  of  10  c.c.  should 
be  diluted  with  recently  boiled  and  cooled  water  to  100  c.c.  and 
10  c.c.  of  this  used  in  the  tests. 

Sulphates  in  the  liquor  may  be  determined  by  placing  10  c.c. 
in  a  covered  beaker,  adding  an  excess  of  strong  hydrochloric 
acid  and  boiling  for  some  time  until  the  odor  of  SO2  is  no  longer 
noticeable.  The  sample  is  then  diluted  and  the  S03  determined 
gravimetrically  as  BaS04. 

Bases  may  be  determined  by  the  following  method  given  by 
Griffin  and  Little.1  Ten  to  twenty  cubic  centimeters  of  the 
acid  are  treated  with  H2SO4  in  slight  excess  in  a  platinum  dish, 
and  evaporated  to  dryness.  The  dry  mass  is  cautiously  ignited 
until  no  more  fumes  come  off,  and  the  residue  cooled  and  weighed 
as  sulphates  of  calcium  and  magnesium. 

Treat  the  sulphates  with  5  c.c.  of  water  and  one  or  two  drops 
of  hydrochloric  acid  and  break  up  all  lumps  with  a  stirring  rod 
Rinse  into  a  beaker  with  as  little  water  as  possible,  add  one  or 
two  drops  of  strong  sulphuric  acid  and  alcohol  equivalent  to 
twice  the  volume  in  the  beaker.  Allow  it  to  stand  with  occa- 
sional stirring  for  an  hour  or  more,  then  filter  off  and  wash  the 
precipitate  first  two  or  three  times  with  60  per  cent  alcohol 
and  finally  with  40  per  cent  alcohol  as  long  as  anything  is  removed 
by  the  treatment.  The  residue  on  the  filter  is  dried,  ignited, 
and  weighed  as  pure  calcium  sulphate. 

Selenium.  As  a  practical  test  for  the  presence  of  selenium 
in  injurious  quantities,  Klason  and  Mellquist 2  seal  up  some  oi 
the  liquor  in  glass  tubes,  from -which  air  has  been  expelled  by 
carbon  dioxide,  and  heat  for  15  hours  at  137°  C.  in  a  bath 
of  boiling  xylene.  If  appreciable  amounts  of  selenium  are  pres- 
ent, the  composition  of  the  liquor  will  be  changed  by  this 
procedure. 

Waste  Liquor.     At  the  end  of  the  cook  the  liquor  in  the 

N 
digester  is  tested  for  total  862  by  means  of  :  -  iodine.     The 

1  Chemistry  of  Paper  Making,  p.  414. 

2  Klason  and  Mellquist:  Papier-Fabr.,  1913,  145. 


TESTS  AND  ANALYSIS  211 

sample  is  generally  drawn  from  about  one-third  the  way  down 
the  digester  and  no  attempt  is  made  to  retain  the  SOz  by  cooling 
the  liquor  as  drawn.  Of  this  hot  liquor  a  5  c.c.  sample  is  gen- 
erally tested. 

For  the  determination  of  free  862  in  waste  liquor,  Stutzer 1 
recommends  the  following:  Place  25  c.c.  of  the  liquor  in  an 
Erlenmeyer  flask,  add  25  c.c.  of  standard  alkali,  then  i  gram  of 
ammonium  chloride  or  nitrate  and  immediately  connect  with  a 
condenser.  Boil  for  just  20  minutes  and  catch  condensate  in 
25  c.c.  of  standard  acid.  The  acid  not  neutralized  by  this  treat- 
ment is  equivalent  to  the  free  acid  in  the  waste  liquor.  , 

1  Stutzer:  Papier  Ztg.,  1911,  36,  5. 


CHAPTER  VH 
GROUND  WOOD   OR  MECHANICAL  PULP 

The  preparation  of  ground  wood  pulp  brings  in  comparatively 
little  of  a  chemical  nature  yet  its  close  relationship  to  the  rest 
of  the  industry  makes  it  desirable  to  include  a  discussion  of  the 
methods  and  general  principles  involved.  The  commercial  man- 
ufacture of  ground  wood  is  generally  not  conducted  according 
to  any  fixed  standards  of  practice,  each  superintendent  or  man- 
ager having  his  own  theories  about  the  best  methods  of  operating. 
For  this  reason  little  reliable  information  was  available  until 
the  Forest  Service  undertook  the  collection  of  data  and  it  is 
upon  their  results  :  that  much  of  the  present  chapter  is  based. 

The  present  method  of  manufacture  has  been  in  use  for  a 
long  time  and  except  for  increased  size  and  capacity  of  grinders 
it  has  changed  but  little  since  its  introduction  in  1867.  The 
process  consists  briefly  in  pressing  blocks  of  wood  against  the 
surface  of  a  grindstone  which  is  also  supplied  with  water  to 
remove  the  pulp  as  fast  as  it  is  made.  The  stones  are  usually 
about  54  ins.  in  diameter  by  27  ins.  face,  but  in  some  recent 
installations  have  been  as  large  as  60  ins.  in  diameter  by  48  ins. 
face.  Up  to  a  few  years  ago  natural  quarried  stones  only  were 
used,  but  many  mills  are  now  experimenting  with  artificial  stones. 
The  wood  to  be  ground  is  placed  in  pockets  in  the  housing  of 
the  stone  in  such  a  way  that  the  logs  are  parallel  with  the  shaft 
on  which  the  stone  is  mounted.  Pistons  operated  by  hydraulic 
pressure  then  force  the  wood  against  the  stone  until  it  is  reduced 
to  pulp.  The  pockets  are  then  recharged  and  the  process  re- 

1  Forest  Service  Bulletin,  Experiments  with  Jack  Pine  and  Hemlock.  Forest 
Service  Bulletin  127,  Grinding  Spruce  for  Mechanical  Pulp.  Forest  Service  Bulle- 
tin 343,  Ground- Wood  Pulp. 

212 


GROUND  WOOD   OR  MECHANICAL  PULP  213 

pea  ted.  There  are  generally  three  or  four  pockets  for  each 
grinder  and  as  they  seldom  become  empty  all  at  once  they  are 
filled  as  necessary  and  the  process  is  thus  continuous. 

There  is  now  on  the  market  a  magazine  grinder  equipped 
with  two  pockets  into  which  the  wood  is  fed  automatically. 
The  Voith  Magazine  Grinder,  shown  in  part  sectional  elevation 


FIG.  31.    THREE-POCKET  GRINDER 

(i)  Grindstone  (2)  Shaft  (3)  Steel  flanges  (4)  Casings  or  side  frames 
(5)  Bridge-trees  (6)  Studs  to  support  (7)  Pockets  (8)  Hydraulic  cylin- 
ders (9)  Piston  rods  (10)  Pressure  foot 

in  Fig.  33  is  of  this  type.  The  advantages  of  this  grinder  are 
said  to  be  (i)  increased  capacity,  (2)  charging  is  automatic  and 
not  subject  to  the  irregularities  of  manual  feeding,  (3)  constant 
load  on  motor  or  turbine  and  (4)  decreased  cost  of  attendance. 
The  pulp  coming  away  from  the  stones  collects  in  pits  under 
the  grinders  and  from  these  pits  it  flows  to  screens  with  one- 
fourth  to  three-fourths  inch  perforations  which  remove  slabs, 
knots,  large  splinters,  etc.  For  satisfactory  operation  of  these 


214 


GROUND  WOOD   OR  MECHANICAL  PULP 


screens  the  stock  should  be  diluted  to  at  least  i  per  cent  dry 
matter.  The  stock  passing  these  coarse  screens  goes  next  to 
the  regular  screens  of  centrifugal  or  diaphragm  type,  and  for 
this  operation  it  should  be  still  further  diluted  to  about  0.25 


FIG.  32.    THREE -POCKET  GRINDER  SECTIONAL  ELEVATION 

per  cent  dry.  It  is  desirable  that  the  diluted  stock  be  passed 
through  a  riffler  or  over  a  sand  settler  before  going  to  the  screens 
as  much  wear  on  the  latter  is  thus  avoided.  The  screened 
stock  is  then  thickened  to  the  proper  consistency  for  use  in  the 
beaters  by  means  of  niters,  wet  machines,  or  some  other  equiva- 


GROUND   WOOD   OR  MECHANICAL   PULP 


215 


lent  device,  or  if  it  is  to  be  sold  in  the  form  of  "laps"  these  are 
made  on  a  wet  press. 

The  chief  factors  which  enter  into  the  production  of  mechani- 
cal pulp  from  any  species  of  wood  are: 

(i)  Surface  of  stone;  whether  rough  or  smooth,  sharp  or  dull, 
or  of  coarse  or  fine  grit. 


Suspension  IJin  for  swinging 
magazine  out  to  harg  stone 


Charging  Floor 


FIG.  33.    VOITH  MAGAZINE  GRINDER 

(2)  Pressure  employed  in  forcing  the  wood  against  the  re- 
volving stone. 

(3)  Peripheral  speed  of  the  stone. 

(4)  Temperature  of  grinding  and  thickness  of  stock  in  the 
grinder  pit. 

(5)  Physical  condition  of  the  wood. 


2l6  GROUND  WOOD  OR  MECHANICAL  PULP 

The  condition  of  the  surface  of  the  stone  depends  on  several 
factors  among  them  being  the  size  and  sharpness  of  the  indi- 
vidual particles  of  grit,  the  ease  with  which  the  binding  mate- 
rial wears  away  and  the  manner  of  dressing  the  stone.  This 
latter  operation  is  performed  by  working  across  the  face  of  the 
stone  small  steel  rolls  or  burrs  of  various  designs  which  roughen 
the  surface  and  form  depressions  through  which  the  ground 
wood  can  escape.  A  great  deal  of  attention  has  been  given  to 
the  designing  of  these  burrs  but  it  appears  that  practically  the 
same  quality  of  pulp  can  be  obtained  under  like  conditions  of 
pressure,  speed  and  temperature  if  the  surface  is  brought  to 
the  same  condition  of  sharpness  of  grit,  regardless  of  whether 
the  design  of  the  markings  is  straight  cut,  spiral  or  diamond 
point.  The  important  thing,  so  far  as  quality  is  concerned,  is 
to  give  the  particles  of  grit  the  correct  treatment,  rather  than 
to  form  a  deeply  grooved  surface. 

The  horsepower  per  ton  of  pulp  varies  inversely  with  the 
sharpness  of  the  stone,  while  the  production  varies  directly 
with  the  sharpness.  Immediately  after  sharpening  a  stone, 
therefore,  the  rate  of  production  is  high  and  the  power  con- 
sumed low,  while  as  the  stone  becomes  dull  the  former  de- 
creases and  the  latter  increases.  The  condition  of  the  surface 
of  the  stone  appears  to  have  very  little  influence  upon  the 
yield  per  cord  unless  it  has  been  made  so  extremely  sharp  that 
more  screenings  are  formed  and  possibly  more  fine  fibre  lost  in 
the  white  water.  With  such  a  surface  the  fibres  are  actually 
ground  to  pieces  and  in  some  instances  they  are  so  short  and 
fine  that  it  is  almost  impossible  to  remove  the  lap  from  the 
wet  machine  press  roll.  Deep  grooving  of  the  surface  of  the 
stone  causes  more  rapid  production  of  pulp  but  at  the  expense 
of  quality,  while  better  pulp  is  produced  by  a  less  sharp  stone 
and  a  greater  application  of  power.  Paper  prepared  from  this 
latter  pulp  has  greater  strength  than  that  from  pulp  ground 
on  very  sharp  stones. 

Next  to  the  surface  condition  of  the  stone  the  factor  most 
influencing  quality  is  the  pressure  at  which  the  wood  is  forced 


GROUND   WOOD   OR   MECHANICAL   PULP    -  217 

against  the  stone.  For  any  given  cylinder  pressure  this  varies 
greatly  with  the  length  and  diameter  of  the  logs,  and  further 
variations  are  caused  by  the  binding  of  the  wood  in  the  pockets 
and  by  fluctuations  in  the  water  pressure  when  the  pistons  are 
raised  or  lowered.  The  result  of  increasing  the  pressure  is  to 
increase  the  power  required  by  the  grinder  and  decrease  the 
power  consumption  per  ton  of  pulp  made.  This  latter  effect 
is  less  noticeable  on  sharp  than  on  dull  stones.  This  result 
is  interesting  because  it  suggests  that  by  carrying  a  high 
pressure  and  using  only  part  of  the  pockets  the  power  con- 
sumption per  ton  can  be  reduced,  or  in  other  words  these  con- 
ditions permit  the  production  of  a  larger  quantity  of  pulp  during 
times  of  low  water,  without  sharpening  the  stone  to  an  unusual 
degree. 

It  has  been  found  that  the  yield  of  pulp  per  100  cu.  ft.  of  solid 
wood  increases  with  increase  of  pressure.  The  screenings  also 
increase,  but  not  so  fast  as  the  total  yield  so  that  there  is  a  net 
gain  of  good  fibre.  The  strength  factor,  or  the  bursting  strength 
per  square  inch  divided  by  the  weight  per  ream,  which  indicates 
the  quality  of  the  pulp,  decreases  quite  rapidly  with  increasing 
pressure. 

The  peripheral  speed  of  the  stone  is  given  little  attention  in 
most  commercial  plants.  When  the  pressure  on  a  pocket  of  the 
grinder  is  removed  the  speed  increases  greatly ,  which  counteracts 
to  a  certain  extent  the  decreased  production  due  to  the  smaller 
number  of  pockets  in  use.  While  this  is  rather  beneficial  than 
otherwise  there  are  conditions  of  operation  which  require  a  fairly 
constant  speed,  and  the  use  of  a  governor  is  therefore  desirable. 
As  would  be  expected  the  power  to  the  grinder  varies  directly 
with  the  speed;  this  is  also  true,  and  to  an  even  greater  extent, 
of  the  production  in  twenty-four  hours.  With  constant  power 
to  the  grinder  the  production  in  twenty-four  hours  is  practically 
constant,  regardless  of  whether  the  pulp  is  produced  at  low 
pressure  and  high  speed  or  at  high  pressure  and  low  speed.  The 
strength  of  the  paper  is  greater  with  pulp  produced  at  high  pres- 
sure and  low  speed  than  with  that  made  at  low  pressure  and  high 


2l8  GROUND  WOOD   OR  MECHANICAL  PULP 

speed.  The  yield  per  cord  and  the  quality  of  the  pulp  are  only 
slightly  influenced  by  the  speed. 

The  effect  of  the  temperature  at  which  mechanical  pulp  is 
produced  has  long  been  a  controversial  point  between  European 
and  American  manufacturers.  The  general  American  practice 
is  to  operate  at  high  temperature  and  it  is  claimed  that  pulp  so 
produced  has  longer  and  stronger  fibres,  is  considerably  tougher 
than  cold-ground  pulp  and  works  "freer"  on  the  paper  machine. 
Cold-ground  pulp,  on  the  other  hand,  is  said  to  be  finer,  more 
free  from  shives  and  to  give  a  better  closed  sheet  of  greater 
opacity  than  hot  ground  pulp. 

Another  factor  which  is  claimed  to  have  an  important  influence 
on  the  paper  produced  is  the  thickness  of  the  pulp  in  the  grinder 
pit,  and  in  actual  operations  this  varies  from  extremely  thick  to 
comparatively  thin. 

Investigation  of  these  two  points  shows  that  varying  the  tem- 
perature from  hot  to  cold  has  little  effect  upon  the  power  con- 
sumption or  power  to  grinder,  but  the  production  in  twenty-four 
hours  is  somewhat  higher  when  grinding  hot.  With  thick  stock 
in  the  grinder  pit  the  power  required  to  rotate  the  grinder  with- 
out load  is  greater  than  with  thin  stock,  but  the  difference,  when 
calculated  to  the  basis  of  power  consumption  per  ton  of  pulp, 
becomes  negligible.  Neither  of  these  two  factors  of  temperature 
and  thickness  of  stock  influences  the  yield  per  cord  of  wood.  The 
quality  of  pulp,  however,  is  affected,  that  produced  at  high  tem- 
perature being  long-fibred,  while  a  fine-fibred  stock  is  more 
easily  secured  by  the  cold  grinding  process. 

The  physical  condition  of  the  wood,  apart  from  any  changes 
induced  by  boiling  or  steaming,  has  a  very  appreciable  influence 
on  the  results  obtained.  For  green  wood  the  average  power  con- 
sumption is  lower  than  for  seasoned  wood  while  the  rate  of  pro- 
duction is  higher.  The  diameter  of  the  bolts  used  and  the  rate 
of  growth  of  the  wood  have  very  little  effect  upon  either  the 
power  consumption  or  the  rate  of  production.  Rapidly  grown 
wood,  as  compared  with  that  which  has  grown  slowly,  yields 
considerably  less  pulp  which  is  softer  though  of  about  the  same 


GROUND  WOOD  OR  MECHANICAL  PULP  219 

strength  as  that  from  slowly  grown  trees.  It  is  generally  recog- 
nized that  green  or  freshly  cut  wood  gives  a  better  product  than 
seasoned  wood,  and  in  the  case  of  white  fir  McNaughton  x  has 
shown  that  pulp  from  young  trees  18  ins.  or  less  in  diameter  is 
whiter  and  stronger  than  that  from  old  trees  of  about  40  ins. 
diameter. 

The  commercial  efficiency  in  converting  rossed  wood  to  pulp 
under  ordinary  conditions  averages  about  88  per  cent.  Of  the 
remaining  12  per  cent  about  2  to  7  per  cent  is  lost  as  screenings 
and  in  the  white  water  as  wood  fibre,  while  the  remaining  5  to 
10  per  cent  must  be  in  the  white  water  as  water  soluble  organic 
or  inorganic  materials. 

The  changes  induced  by  boiling  or  steaming  the  wood  before 
grinding  very  profoundly  influence  the  product  obtained.  The 
color  of  the  pulp  is  darker  than  that  from  unsteamed  wood  and 
the  fibres  are  much  longer  and  better  separated,  resulting  in  a 
stronger  product.  The  changes  in  color  and  physical  character 
of  the  pulp  are  practically  identical,  provided  the  temperature 
and  duration  of  the  cooking  are  the  same,  whether  the  logs  are 
steamed  or  boiled  while  immersed  in  water.  Steaming  has  the 
advantage  over  boiling  in  that  less  heat  is  necessary  and  the  con- 
densed liquors  are  drawn  off  in  concentrated  form  which  is  a  ben- 
efit where  recovery  of  by-products  is  attempted.  As  soon  as 
steaming  starts  the  formation  of  acid  commences  and  increases 
up  to  the  end  of  eight  hours  treatment.  Both  acetic  and  formic 
acids  are  produced,  in  the  ratio  of  six  acetic  to  one  formic.  Spruce 
gives  0.213  per  cent  of  acetic  acid  and  pine  yields  similar  amounts. 
After  two  hours  steaming  reducing  sugars  appear  and  eventually 
amount  to  about  0.25  per  cent  of  the  dry  wood. 

The  pressure  and  duration  of  steaming  are  important  factors 
to  control  since  they  have  a  great  influence  on  the  color,  strength 
and  yield  of  pulp.  Increasing  both  time  and  steam  pressure 
increases  the  strength  of  the  pulp  but  makes  it  much  darker  in 
color  while  at  the  same  time  the  yield  is  much  decreased  because 
of  the  greater  solvent  power  of  the  water. 

1  Paper,  Nov.  i,  1916,  p.  13. 


220  GROUND  WOOD  OR  MECHANICAL  PULP 

A  study  of  the  various  factors  in  the  grinding  of  steamed  spruce 
wood  has  brought  out  a  number  of  very  interesting  facts.  The 
power  required  per  ton  of  pulp  is  at  least  25  per  cent  greater  than 
that  used  in  grinding  untreated  wood,  and  the  maximum  power 
per  ton  is  reached  when  the  wood  is  cooked  for  six  hours.  This 
holds  true  for  cooking  pressures  between  o  and  75  Ibs.  gauge  pres- 
sure. With  the  same  length  of  cooking,  wood  which  is  treated 
at  high  pressure  requires  more  power  per  ton  of  pulp  than  that 
which  has  been  cooked  at  lower  pressures,  while  with  a  fixed 
amount  of  power  to  the  grinder  the  amount  of  pulp  produced  is 
less  at  high  pressure  and  low  speed  than  it  is  at  low  pressure  and 
high  speed. 

The  pulp  made  by  grinding  steamed  wood  can  be  used  for 
different  purposes,  depending  on  the  nature  of  the  grinding 
process.  If  a  sharp  and  coarse  stone  is  used  a  large  number  of 
shives  will  be  present  and  the  pulp  will  serve  for  the  manufacture 
of  box  boards  or  similar  products.  When  ground  to  a  finer  state, 
and  mixed  with  a  small  amount  of  chemical  fibre  a  bogus  kraft 
paper  can  be  produced  which  will  serve  for  a  cheap  wrapping 
paper.  Tests  on  papers  made  from  steamed  and  unsteamed 
woods  show  that  the  steamed  pulps  give  a  higher  percentage  of 
stretch  than  the  unsteamed  even  though  the  latter  are  mixed 
with  20  per  cent  of  sulphite  spruce  fibre.  Like  chemical  pulps 
steamed  ground  wood  is  considerably  influenced  by  beating 
treatments  and  variations  in  the  latter  cause  marked  variations 
in  the  strength  of  the  paper.  With  prolonged  beating  the  paper 
becomes  more  brittle  but  gives  higher  strength  tests. 

The  boiling  or  steaming  of  wood  results  in  the  formation  of  a 
natural  size  from  some  of  its  constitutents  and  this  sizing  action 
is  particularly  noticeable  in  the  production  of  pulps  from  the 
hardwoods  —  birch  and  aspen  —  which  are  not  naturally  pitchy. 
All  paper  produced  from  cooked  woods,  pulped  by  the  mechanical 
process,  shows  the  characteristic  water-resistant  qualities  and 
hardness  of  hard  sized  papers. 

While  spruce  is  the  standard  wood  for  the  manufacture  of 
mechanical  pulp  the  supply  of  this  wood  is  decreasing  so  rapidly 


GROUND  WOOD   OR  MECHANICAL  PULP 


221 


that  some  substitute  must  be  found.  With  this  end  in  view  a 
long  series  of  tests  has  been  made  on  a  practical  scale  by  the 
Forest  Service  l  and  the  pulps  made  run  into  paper  and  tested  for 
printing  qualities  on  newsprint  presses.  The  following  table 
gives  the  common  and  scientific  names  of  the  woods  used,  the 
yield  of  bone  dry  fibre  from  100  cu.  ft.  of  solid  rossed  wood  and 
the  color  rating,  No.  i  being  the  best  color  and  No.  23  the  poorest. 


Common  name 

Scientific  name 

Bone  dry  fibre 
per  100  cu.  ft. 

Color 
rating 

Balsam  fir  

A  bies  balsamea  

Lbs. 
IQIO 

Q 

Red  fir 

'        magnified 

IQI  ^ 

2O 

White  fir     . 

concolor 

2OOO 

IO 

Alpine  fir 

lasiocarpa 

2o6o 

I 

Amabilis  fir  

amabilis 

1870 

1  3 

Grand  fir         

grandis 

ICKO 

5" 

Noble  fir  

nobilis  .  . 

IQ2O 

I  r 

Eastern  hemlock  
Western  hemlock  
Tamarack  

Tsuga  canadensis  
heterophylla  
Larix  laricina  

2030 
2l6o 
262O 

19 
22 
21 

Western  larch 

"     occidentalis 

2IOO 

S-2 

Lodgepole  pine 

Pinus  murrayana  1 

IQ2O 

I  2 

Lodgepole  pine 

murrayana  2 

2I*1O 

6 

Western  yellow  pine 

ponderosa 

2o6o 

1  1 

Jack  pine 

divaricata.  .  . 

22OO 

14. 

Loblolly  pine  

taeda  

2  COO 

7 

White  pine  

strobus  

1885 

8 

Engelmann  spruce  
Sitka  spruce  
White  spruce  
Aspen 

Picea  engelmanni  
sitchensis  
'      canadensis  
Populus  tremuloides 

2000-2250 
2IOO 
24OO 
22OO 

3 
18 

2 

16 

White  birch 

Betula  papyri/era 

2QCO 

17 

Black  gum 

Nyssa  sylvatica 

2600 

Wood  from  California. 


Wood  from  Montana. 


In  these  trials  very  little  difficulty  was  experienced  in  pro- 
ducing pulp  from  the  woods  tested.  With  the  conifers  grinding 
could  be  done  under  practically  the  same  conditions  employed 
for  spruce.  All  the  substitutes,  with  the  possible  exception  of 
noble  fir  and  amabilis  fir,  require  the  use  of  more  power  per  ton 
of  pulp  than  does  spruce.  The  best  results  were  generally 
obtained  by  grinding  on  a  somewhat  dull  stone  with  high  pressure 
and  rather  slow  speed. 

1  Bull.  No.  343,  U.  S.  Dept.  of  Agriculture. 


222  GROUND  WOOD  OR  MECHANICAL  PULP 

Of  the  woods  tried  all  of  the  firs  yield  pulp  suitable  for  news- 
print purposes;  hemlock  gives  a  short  fibre  and  much  care  is 
necessary  in  grinding;  western  hemlock  is  much  superior  to 
eastern.  Tamarack  gives  a  good  quality  of  pulp  except  for  its 
color  which  is  grayish  green,  while  western  larch  yields  a  very 
inferior  pulp,  shivey  and  of  poor  color.  The  pines  yield  pulp 
which  could  be  used  for  newsprint  work  though  there  is  a  tend- 
ency toward  softness.  The  one  exception  is  loblolly  pine  which 
gives  an  inferior  pulp  which  would  find  use  only  as  a  filler.  Of  the 
hardwoods  aspen  gives  a  satisfactory  pulp  if  a  large  amount  of 
power  is  employed  in  grinding.  When  mixed  with  spruce  it 
operates  very  well.  White  birch  yields  a  short,  but  very  fine 
fibre,  which  has  a  pinkish  tinge;  it  could  be  used  as  a  filler  in 
certain  grades  of  paper.  Black  gum  gives  a  fibre  resembling  in 
many  ways  that  from  white  birch.  It  is  very  short  but  forms  a 
tougher  sheet  than  coniferous  fibres  of  the  same  length.  This 
pulp  is  not  promising  for  newsprint  paper  but  could  be  used  as  a 
filler  or  mixed  with  pulp  of  a  better  grade. 

The  ground  wood  process  has  received  much  attention  from 
investigators  with  the  object  of  producing  fibre  which  could  be 
used  in  making  news  paper  without  the  addition  of  sulphite. 
Bache-Wiig  1  has  patented  a  process  whereby  the  blocks  of  wood 
are  heated  in  a  solution  of  salt  and  then  ground  as  usual.  As,  in 
many  cases,  the  salt  does  not  penetrate  the  entire  block  the 
resulting  pulp  is  a  mixture  of  untreated  and  treated  fibres.  The 
claims  for  this  process  are  that  less  power  is  required  and  the 
fibre  is  longer  and  stronger  and  of  better  color.  According  to 
another  process 2  the  wood  blocks  are  placed  in  a  digester  which 
is  partially  evacuated,  then  treated  under  pressure  with  sulphur 
dioxide  and  finally  cooked  with  water,  salt  solution  or  bisulphite 
liquor.  Wood  thus  treated  gives,  on  grinding,  a  pulp  suitable  for 
making  news  paper  without  the  addition  of  sulphite. 

Henckel 3  proposes  cooking  the  logs  with  a  caustic  soda  solu- 

1  U.  S.  patent  913,679. 

2  Bache-Wiig:  Paper,  1916,  No.  21,  p.  18. 

3  Henckel:  Austrian  patent  34,816. 


GROUND  WOOD   OR  MECHANICAL  PULP  223 

tion  of  3°  to  5°  Be.  for  three  or  four  hours  under  pressure  and  then 
grinding  as  usual.  The  claims  for  this  process  are  better  fibre,  less 
power  and  greater  yield.  It  is  difficult  to  see  how  the  yield 
can  be  increased  by  treating  with  a  solution  having  such  strong 
solvent  powers  as  a  caustic  soda  solution. 

A  modification  which  has  recently  attracted  much  attention  is 
that  for  producing  white  ground  wood  by  the  Enge  process.1 
According  to  this  process  the  logs  are  placed  in  a  boiler  which  is 
then  completely  filled  with  water.  The  temperature  is  raised  by 
direct  or  indirect  steam  to  176°  to  257°  F.,  steam  is  shut  off  and 
hot  or  cold  water  pumped  in  to  raise  the  pressure  to  147  Ibs.  or 
more,  which  is  maintained  for  five  to  eight  hours.  The  higher 
the  pressure  carried  the  higher  can  the  temperature  go;  good 
conditions  are  230°  F.,  and  six  hours  at  147  to  176  Ibs.  per  square 
inch.  Following  this  treatment  the  grinding  is  completed  on 
ordinary  stones  as  usual.  The  advantage  of  this  process  is 
somewhat  doubtful,  for  although  the  pulp  can  be  made  into  news 
paper  alone,  yet  the  extra  cost  for  steaming,  labor,  etc.,  just  about 
counterbalances  the  saving  in  cost  of  sulphite  fibre. 

With  any  method  of  grinding  close  control  of  the  process  is 
essential  if  a  uniform  product  is  to  be  made.  A  very  simple 
method  for  obtaining  such  control  is  to  examine  the  image  of  the 
fibres  when  thrown  on  a  screen  by  means  of  a  lantern.  The  pulp 
may  be  mixed  with  a  little  aniline  dye  so  that  a  sharper  image 
may  be  obtained.  A  little  of  the  pulp  is  then  placed  between  two 
glass  plates  in  such  a  density  that  the  individual  fibres  may  be 
observed,  and  its  image  thrown  upon  a  white  screen.  The  best 
magnification  is  about  40  diameters  and  when  enlarged  to  this 
extent  it  is  very  easy  to  tell  the  relative  proportions  of  "  fluff," 
long  fibre,  shives,  slivers,  etc.  This  method  is  in  operation  in 
one  of  the  most  progressive  mills  in  Canada  and  is  very  highly 
recommended.  Samples  from  each  stone  are  examined  every 
two  hours  and  the  condition  of  the  stone  and  the  work  it  is  doing 
are  thus  accurately  known,  making  it  possible  to  sharpen  the 

1  German  patents  20,860  and  20,932,  E  VII,  55a. 


224  GROUND   WOOD   OR  MECHANICAL  PULP 

stone  when  it  is  necessary  and  keep  the  pulp  much  more  nearly 
uniform. 

Another  control  test  which  is  in  actual  use  and  is  giving  very 
good  results  is  that  of  the  sediment  tester  described  by  Fishburn 
and  Weber.1  In  this  test  a  mixture  of  5  grams  bone  dry  pulp 
and  500  c.c.  of  water  is  placed  in  a  graduated  tube  with  a  woven 
wire  bottom  and  the  time  required  to  drain  down  to  a  definite 
mark  is  noted.  The  standard  time  for  news  grade  wood-pulp  is 
80  seconds  and  if  it  is  ground  in  such  a  way  as  to  give  a  test  of 
70  seconds  trouble  is  experienced  on  the  paper  machine. 

The  bleaching  of  wood  pulp  cannot  be  performed  by  hypo- 
chlorites  or  other  oxidizing  agents  since  all  the  lignin  and  other 
incrusting  matters  are  still  present.  Its  color  can  be  consider- 
ably improved  by  treating  with  sulphurous  acid  or  a  bisulphite. 
This  is  regularly  done  in  European  practice  by  moistening  the 
pulp  with  a  solution  of  sodium  bisulphite  as  it  is  wound  up  on  the 
press  roll  of  the  wet  machine.  According  to  Schutz 2  about  2  to 
3  per  cent  is  used.  The  action  requires  time  and  the  color  is  not 
so  bright  as  that  of  bleached  chemical  pulp.  All  woods  are  not 
equally  susceptible  to  improvement  in  color  by  this  process; 
hemlock  and  tamarack,  for  instance,  are  not  so  good  as  poplar  and 

spruce. 

1  Paper,  Oct.  n,  1916,  p.  13. 

2  Schutz:  Paper,  Feb.  4,  1917,  p.  64. 


CHAPTER  VIII 
BLEACHING 

All  of  the  commercial  processes  for  isolating  the  fibrous  cellu- 
loses for  paper  making  fail  to  produce  a  perfectly  pure  material 
since  it  is  always  associated  with  a  small  amount  of  the  in- 
crusting  matter  originally  present  in  the  raw  material  and  gen- 
erally also  with  coloring  matters,  which  either  escaped  destruc- 
tion during  the  process  or  were  formed  by  it.  The  object  of 
bleaching  is  the  destruction  or  removal  of  such  undesirable 
impurities  so  that  the  natural  white  color  of  the  pure  cellulose 
may  become  evident.  The  process  of  bleaching  is  essentially 
one  of  oxidation  and  the  success  attained  depends  on  the  fact 
that  the  accompanying  impurities  are  attacked  and  resolved 
into  soluble  products  much  more  easily  than  the  comparatively 
inert  cellulose  of  which  the  impure  fibre  is  largely  composed. 
Many  different  oxidizing  agents  can  be  utilized  in  the  bleach- 
ing process  and  a  number  of  them  have  been  applied  with  more 
or  less  success,  but  practically  all  commercial  work  is  performed 
by  chlorine,  or  some  of  its  compounds,  which  in  the  presence  of 
moisture  tend  to  liberate  oxygen. 

Chlorine.  Chlorine  is  a  greenish  yellow  gas,  darkening  in 
color  as  the  temperature  rises.  It  has  a  pungent  and  irritating 
odor  and  cannot  be  inhaled  as  it  attacks  the  membranes  of  the 
throat  and  nose.  Its  atomic  weight  is  35.457  and  a  liter  of  it 
at  o°  C.  and  760  mm.  pressure  weighs  3.1691  grams.  One  vol- 
ume of  water  at  15°  C.  and  760  mm.  pressure  absorbs  2.37 
volumes  of  chlorine.  At  15°  C.  and  6  atmospheric  pressure  it  is 
converted  into  a  clear  yellow  liquid  of  specific  gravity  1.33, 
which  is  not  miscible  with  water.  When  perfectly  dry  it  does 
not  attack  iron,  which  enables  it  to  be  stored  and  shipped  in 

225 


226  BLEACHING 

wrought-iron  cyclinders.     Dry  chlorine  is  also  devoid  of  bleach- ' 
ing  properties  as  may  be  shown  by  passing  the  dry  gas  over  a 
piece  of  litmus  paper,  or  a  cloth  dyed  a  delicate  shade;   so  long 
as  moisture  is  absent  no  bleaching  action  takes  place,  but  on 
the  addition  of  water  the  color  is  at  once  destroyed. 

Gas  Bleaching.  In  bleaching  with  chlorine  gas  the  material 
to  be  treated  must  be  placed,  while  in  a  moist  condition,  in  a 
receptacle  which  is  capable  of  being  tightly  closed.  It  is  then 
subjected  to  the  action  of  the  gas,  either  generated  by  means 
of  manganese  peroxide  or  obtained  from  some  other  source.  If 
the  material  to  be  bleached  is  very  shivey,  gas  bleaching  mate- 
rially assists  in  the  production  of  clean  stock  as  it  tends  to 
resolve  the  woody  matter  more  completely  than  does  bleaching 
powder  solution.  It  is  also  very  efficient  in  removing  metallic 
particles.  Gas  bleaching  has  in  the  past  been  applied  to  rag 
and  rope  stock,  wood  pulp,  straw,  etc.,  but  little  information  is 
available  to  show  how  much  of  the  gas  is  actually  used  up  in 
the  bleaching.  Beadle  and  Stevens  l  cite  a  case  of  a  cotton  rag 
half-stuff  which  normally  required  12  per  cent  of  bleaching 
powder  but  in  which  a  better  color  was  produced  by  treatment 
with  2  per  cent  of  chlorine  followed  by  2  per  cent  of  bleach. 
In  this  case  2  per  cent  of  chlorine  replaces  10  per  cent  of  bleach- 
ing powder,  or  is 'equivalent  to  3.5  per  cent  of  chlorine  in  the 
form  of  bleaching  powder.  Experiments  by  the  author  on  a 
sample  of  soda  hemlock  which  could  not  be  satisfactorily 
bleached  with  hypochlorite  solution  showed  that  4  per  cent  of 
chlorine  followed  by  5  per  cent  of  bleach  gave  a  good  color 
and  that  in  this  case  2  per  cent  of  chlorine  was  equivalent  to 
3  per  cent  in  the  form  of  hypochlorite.  In  spite  of  its  good 
bleaching  efficiency  the-  process  is  seldom  used  because  of  the 
difficulty  of  maintaining  tight  apparatus  and  the  general  in- 
convenience involved;  it  is  never  employed  in  this  country. 

Hypochlorites.  When  chlorine-  is  passed  into  an  aqueous 
solution  of  an  alkali,  or  alkaline  earth,  a  hypochlorite  or  hypo- 

1  J.  Soc.  Chem.  Ind.,  1914,  p.  727. 


HYPOCHLORITES  227 

chlorous  acid  is  formed  according  to  the  equations: 

2  KOH  +  2  Cl  =  KOC1  +  KC1  +  H2O 
KOH  +  2  Cl  =  KC1  +  HOC1. 

If  it  is  passed  into  a  suspension  of  calcium  carbonate,  hypo- 
chlorous  acid  only  is  formed: 

CaC03  +  H20  +  4  Cl  =  CaCl2  +  CO2  +  2  HOC1. 

The  first  bleaching  compound  known,  eau  de  Javel,  was 
made  in  1789  at  the  Javel  works  near  Paris  by  passing  chlorine 
gas  into  a  solution  of  crude  potassium  carbonate.  In  1798 
Tennant  patented  a  bleach  liquor  prepared  by  passing  the  gas 
into  caustic  soda  or  milk  of  lime  and  this  method  is  still  very 
largely  employed  where  chlorine  can  be  produced  cheaply  and 
the  bleach  solution. used  on  the  spot. 

According  to  Higgins  1  hypochlorites  and  hypochlorous  acid 
bleach  because  of  their  readiness  directly  to  produce  oxygen 
and  to  a  lesser  extent  because  of  the  generation  of  nascent:: 
chlorine.  As  the  bleaching  with  hypochlorous  acid  proceeds, 
hydrochloric  acid  accumulates  and  reacts  with  the  hypochlo- 
rous acid  according  to  the  equation,  HOC1  +  HC1  =  H20  +  C12. 
When  a  hypochlorite  is  used  the  acid  formed  is  used  in  liberat- 
ing more  hypochlorous  acid.  It  has  been  shown  experimentally 
that  the  removal  of  free  hydrochloric  acid  from  either  hypo- 
chlorous  acid  or  chlorine  water  by  means  of  calcium  carbonate 
results  in  an  acceleration  of  the  bleaching  action.  Higgins 2 
has  also  shown  that  the  addition  of  calcium,  barium  or  sodium 
chloride,  or  of  sodium  or  potassium  fluoride  to  a  hypochlorite 
solution  causes  an  initial  increase  in  rate  of  bleaching,  but  that 
this  acceleration  soon  ceases  and  the  normal  rate  of  bleaching 
ensues.  This  action  is  due  to  the  formation  of  nascent  chlorine: 
HOC1  +  NaCl  ^  NaOH  +  C12.  The  calcium  chloride  formed 
during  the  action  of  the  bleaching  powder  is  negligible  but 
when  calcium  chloride  is  added  during  the  process  it  always  has 

1  J.  Soc.  Dyers  and  Colorists,  1914,  30,  326. 

2  J.  Soc.  Chem.  IndL,  1913,  32,  350. 


228  BLEACHING 

a  stimulating  effect.  This  effect  of  adding  salt  probably  ex- 
plains in  part  the  claims  for  greater  efficiency  which  many 
observers  have  made  for  electrolyzed  salt  solutions  since  the 
latter  always  contain  a  large  proportion  of  undecomposed 
chloride. 

Bleaching  Powder.  The  bleaching  solutions  first  prepared 
by  Tennant  proved  difficult  to  keep  and  transport  and  in  1799 
he  introduced  a  great  improvement  by  absorbing  chlorine  gas 
in  slaked  lime,  thus  forming  bleaching  powder,  which  is  still  the 
most  important  commercial  bleaching  agent. 

The  quality  of  the  lime  used  in  making  bleaching  powder  is 
of  importance,  a  fat  lime  which  slakes  quickly  and  gives  a  fine, 
light  powder  being  most  suitable  since  it  absorbs  the  gas  more 
quickly  and  gives  a  better  keeping  powder  than  a  poorer  lime. 
Careful  slaking  is  essential  since  the  total  moisture  in  the  chlo- 
rine and  the  lime  should  be  about  28  per  cent  or  about  4  per  cent 
over  that  necessary  to  give  calcium  hydrate,  Ca(OH)2.  Well- 
made  bleaching  powder  should  be  a  pure  white  powder  which, 
if  of  high  strength,  may  contain  some  lumps.  These,  however, 
should  be  of  the  same  quality  as  the  powder  and  should  not 
contain  hard  cores  of  calcium  hydrate.  In  the  air  it  absorbs 
moisture  and  carbon  dioxide  and  is  finally  converted  into  a 
sticky,  grayish  mass.  According  to  Lunge  the  composition  of 

bleaching  powder  is  best  expressed  by  the  formula,  Ca  ^        • 

On  dissolving  the  powder  this  is  changed  into  Ca02Cl2  and 
CaCl2. 

The  value  of  bleaching  powder  depends  on  the  percentage  of 
chlorine  present  as  hypochlorite,  or,  as  it  is  generally  expressed, 
"  available  chlorine."  Bleach  made  in  cold  weather  may  con- 
tain as  much  as  38  per  cent  available  chlorine  but  in  hot  weather 
it  is  at  times  difficult  to  prepare  it  with  even  35  per  cent.  In 
laboratory  experiments  it  has  been  made  with  as  high  as  43.1 
per  cent  available  chlorine.  The  powder  gradually  loses  strength, 
even  in  the  absence  of  air,  while  the  presence  of  air,  moisture  or 
heat  causes  it  to  deteriorate  much  more  rapidly.  The  shaking 


BLEACHING  POWDER 


22Q 


incident  to  transportation  also  causes  more  loss  than  would 
occur  under  normal  conditions  of  quiet  storage,  hence  the 
strength  is  usually  guaranteed  only  at  the  place  of  shipment. 
In  1886  Pattinson  l  completed  a  very  careful  series  of  tests  to 
show  the  deterioration  of  bleaching  powder.  He  stored  three 
casks  of  bleach  in  a  cave  and  tested  them  at  intervals  of  a 
month  for  eleven  months,  at  the  same  time  keeping  a  record  of 
the  temperatures  by  means  of  maximum  and  minimum  ther- 
mometers. This  record  shows  the  temperature  to  have  been 
comparatively  low  and  quite  uniform  during  the  entire  period, 
the  highest  being  62°  F.  and  the  lowest  38°  F.  Tests  of  the 
samples  taken  from  the  casks  showed  a  gradual  and  regular 
loss  of  available  chlorine  which  at  the  end  of  the  investigation 
amounted  to  about  3  per  cent.  The  complete  analysis  of  each 
of  the  cask  samples  at  the  beginning  and  end  of  the  experiment 
is  given  in  the  table  below: 


Jan.  29,  1885 

Jan.  5.  1886 

A 

B 

C 

A 

B 

C 

Available  chlorine  

37-00 

o-35 
0.25 

44-49 
0.40 
0.40 
0.18 

0.48 
16.45 

38.30 

o-59 
0.08 

43-34 
0.31 
0.30 
0.30 

0-45 
16.33 

36.00 
0.32 
0.26 
44.66 

0-43 
0.50 
0.48 

0-35 
17.00 

33-80 
2-44 
o.oo 

43-57 
0.31 
0.50 
0.80 

0.40 
18.18 

36.10 
2.42 
O.OO 

42.64 
0.36 
0.40 
1.48 

0.40 
17.20 

32.90 

i-97 
o.oo 

43-65 
0.38 

0.50 
i-34 

o-37 
18.89 

Chlorine  as  chloride 

Chlorine  as  chlorate 

Lime 

^Magnesia 

Silicious  matter 

Carbon  dioxide 

Alumina,  ferric  oxide  and  oxide  of 
manganese      

Water  and  loss  

Total  chlorine                            .    .    . 

IOO.OO 

37.60 

IOO.OO 

38.97 

IOO.OO 

36.58 

100.00 

36.24 

100.00 

37-52 

100.00 

34-87 

It  is  seldom  that  bleach  can  be  stored  for  any  length  of 
time  at  a  temperature  as  low  as  60°  F.,  especially  during  the 
summer  when  the  greatest  loss  of  strength  is  likely  to  take 
place.  It  should,  however,  be  kept  in  as  cool  and  dry  a  loca- 
tion as  possible  and  any  damaged  casks  should  be  used  first  as 

1  J.  Soc.  Chem.  Ind.,  1886,  587. 


230  BLEACHING 

the  consequent  exposure  of  the  powder  permits  more  rapid 
deterioration  to  take  place.  Another  factor  which  has  a  con- 
siderable influence  on  the  rate  at  which  the  powder  loses  strength 
is  the  quality  of  the  cask  in  which  it  is  packed.  The  best  casks 
are  those  made  from  oak  staves  which  are  about  an  inch  in 
thickness.  Lighter  staves  and  other  woods  are  often  used  but 
soft  woods  which  shrink  badly  when  exposed  to  the  sun  should 
be  avoided  as  they  permit  entrance  of  moisture  if  the  casks  are 
subsequently  exposed  to  rain.  In  recent  years  the  powder  is 
often  packed  in  thin,  sheet-iron  drums  which  have  been  found 
to  give  fairly  good  satisfaction.  As  these  are  not  intended  for 
refilling  they  are  made  as  thin  as  is  consistent  with  sufficient 
strength  for  handling  and  they  are  therefore  lighter  and  occupy 
less  space  than  wooden  casks.  Such  drums  will,  however,  rust 
through  in  time  and  allow  the  bleach  to  deteriorate. 

The  preparation  of  bleaching  powder  solutions  has  been  care- 
fully studied  by  Carey  and  Muspratt.1  They  found  that  long 
agitation  of  the  powder  with  water  caused  slow  settling  and  a 
larger  volume  of  sludge  and  that  the  solution  of  the  calcium 
hypochlorite  was  as  complete  with  twenty  minutes  agitation  as 
it  was  in  a  longer  time.  The  temperature  was  also  found  to 
exert  an  important  influence  as  at  higher  temperatures  the 
settling  was  more  rapid  and  the  volume  of  sludge  less.  It  was 
found  safe  to  prepare  solutions  at  90°  F.,  but  75°  to  80°  F.  was 
considered  better  practice.  The  sludge,  after  drawing  off  the 
strong  bleach  solution,  should  be  given  a  washing  by  filling  the 
tank  with  water,  agitating  a  few  minutes  and  again  allowing 
it  to  settle.  The  weak  liquor  thus  prepared  may  be  used  to 
dilute  the  strong  first  liquor  or  for  mixing  with  another  charge 
of  powder.  The  strength  of  solution  usually  prepared  is  4.5° 
to  5°  Be.,  this  together  with  the  washings  gives  a  liquor  of 
about  3°  Be.  which  is  a  satisfactory  strength  for  practical  work. 

The  sludge,  or  residue,  from  dissolving  bleaching  powder  con- 
sists almost  entirely  of  calcium  hydroxide  but  it  is  not  possible 
to  remove  the  last  traces  of  available  chlorine  without  excessive 

1  J.  Soc.  Chem.  Ind.,  1903,  674. 


BLEACHING  POWDER   SOLUTIONS  231 

washing.  With  careful  work  such  losses  should  not  be  over 
0.3  to  0.4  per  cent.  The  sludge  should  be  tested  for  available 
chlorine  at  frequent  intervals  as  considerable  loss  may  occur  if 
the  washing  is  incomplete.  The  volume  occupied  by  the  sludge 
will  necessarily  vary  with  different  powders  and  different  meth- 
ods of  dissolving  but  under  normal  conditions  it  should  not 
exceed  5  cu.  ft.  per  100  Ibs.  of  powder. 

A  solution  of  bleaching  powder  is  subject  to  decomposition 
of  a  nature  similar  to  that  taking  place  in  the  powder  itself. 
This  change  is  hastened  by  heat,  light  and  air.  Lunge  and 
Landolt l  examined  the  stability  of  bleach  solutions  and  found 
that  when  kept  in  the  dark  and  away  from  air  no  change  took 
place  in  24  days  and  only  a  very  slight  change  at  the  end  of  33 
days;  when  stored  in  the  dark,  but  in  open  vessels,  one-eighth 
of  its  strength  was  lost  in  33  days  and  when  kept  in  diffused 
daylight  75  per  cent  of  its  strength  was  lost  in  the  same  time. 
Presence  of  acid  or  excess  chlorine,  or  exposure  to  direct(  sun- 
light causes  still  more  rapid  decomposition.  Tests  by  the  author 
on  a  very  strong  bleach  solution  —  82  grams  available  chlorine 
per  liter  —  prepared  by  absorbing  chlorine  in  milk  of  lime, 
showed  that  when  kept  in  a  flask  covered  loosely  with  a  watch 
glass  and  exposed  to  diffused  daylight  only  2  per  cent  of  its 
strength  was  lost  in  eight  days.  Higgins  2  has  compared  bleach- 
ing-powder  solutions  with  those  prepared  electrolytically,  and 
with  sodium  hypochlorite  prepared  by  treating  bleach  solution 
with  soda  ash,  and  found  all  equally  stable.  All  of  these  in- 
vestigations point  to  the  desirability  of  storing  bleach  solutions 
in  tall,  narrow  tanks,  where  they  will  be  exposed  to  light  as 
little  as  possible. 

The  action  of  bleaching  powder  solutions  on  metals  has  been 
studied  by  White.3  He  found  that  antimony  and  cadmium 
were  not  attacked,  lead  and  zinc  were  acted  on  only  very  slowly 
because  of  impurities  such  as  iron  and  arsenic,  while  aluminum 

1  Chem.  Ind.,  1885,  343. 

2  J.  Soc.  Chem.  Ind.,  1911,  185. 

3  J.  Soc.  Chem.  Ind.,  1903,  132. 


232  BLEACHING 

was  acted  on  very  slowly  in  wire  form  but  rapidly  when  present 
as  filings.  Nickel  and  iron  were  rapidly  attacked  with  evolu- 
tion of  oxygen  and  formation  of  the  respective  hydroxides,  while 
copper  was  slowly  attacked  and  tin  very  slowly,  about  one- 
twentieth  of  the  rate  of  action  on  iron.  The  author's  tests  on 
strong  bleach  solutions  showed  that  in  five  days  the  presence  of 
metallic  zinc  in  contact  with  the  solution  caused  a  loss  of  10.5 
per  cent  of  the  available  chlorine  while  lead  caused  a  loss  of 
3.6  per  cent  and  ferric  oxide  6  per  cent.  Solutions  of  similar 
strength  kept  for  the  same  length  of  time  away  from  contact 
with  all  metallic  substances  lost  none  of  their  available  chlorine. 
Where  electric  power  is  available  bleach  solutions  are  often 
prepared  by  electrolyzing  a  strong  salt  solution  and  absorbing 
the  chlorine  in  milk  of  lime.  Such  solutions  have  all  the  prop- 
erties of  those  made  by  dissolving  bleaching  powder.  If  a 
sufficient  excess  of  lime  is  used  and  the  temperature  is  not 
allowed  to  rise  too  high  it  is  possible  to  prepare  solutions  con- 
taining 250  grams  per  liter  of  35  per  cent  bleach  with  96  per  cent 
of  the  chlorine  in  the  available  form.  Such  solutions  are  of 
course  too  strong  to  use  in  actual  bleaching  operations  but  they 
are  economical  of  storage  room  and  may  be  shipped  to  consid- 
erable distances  in  tank  cars.  In  cold  weather  very  strong 
solutions  of  bleach  occasionally  deposit  a  considerable  quan- 
tity of  crystals  which  consist  of  solid  calcium  hypochlorite. 
Some  of  this  solid  hypochlorite  is  also  present  in  the  mud  which 
separates  during  the  preparation  of  solutions  containing  225 
grams  per  liter,  or  more,  of  35  per  cent  bleach.  This  crystalline 
form  is  very  unstable  and  its  preparation  has  never  proved 
practical  or  desirable.  In  preparing  strong  bleach  solutions 
there  is  occasionally  a  lot  which  turns  pink.  This  was  formerly 
supposed  to  be  due  to  the  presence  of  manganese  but  Tarugi l 
claims  that  it  is  caused  by  iron  and  has  succeeded  in  causing  it 
by  warming  a  bleach  solution  to  -which  a  little  soluble  iron  salt 
has  been  added.  Elledge,2  on  the  other  hand,  has  proved  that 

1  Chem.  Centr.,  1905,  584,  1902,  718. 

2  Elledge:  J.  Ind.  Eng.  Chem.,  1916,  8,  780. 


ELECTROLYTIC   BLEACH  233 

it  can  be  caused  by  traces  of  manganese  and  it  seems  probable 
that  it  may  be  caused  at  times  by  either  one  of  these  substances. 

Electrolytic  Bleach.  Besides  the  various  calcium  hypochlo- 
rite  solutions  there  are  numerous  devices  for  the  electrolysis  of 
salt  solutions  and  the  direct  application  of  the  sodium  hypo- 
chlorite  solutions  thus  obtained.  The  most  celebrated  of  these 
is  the  Hermite  process  which  originally  employed  a  solution  of 
magnesium  chloride  but  in  which  salt  was  later  used  almost 
exclusively.  According  to  this  plan  the  solution  was  first  elec- 
trolyzed  and  then  passed  through  the  material  to  be  bleached 
and  back  to  the  electrolyzer,  thus  keeping  up  a  continuous  cir- 
culation. This  continuous  process  can  only  be  applied  to  rag 
stock  as  the  impurities  dissolved  in  bleaching  esparto  or  chemi- 
cal wood  pulp  soon  contaminate  the  solution  to  such  an  extent  as 
to  interfere  with  its  proper  operation.  The  Hermite  process  is 
probably  not  used  in  this  country. 

Many  other  schemes  for  the  use  of  electrolyzed  salt  solutions 
have  been  proposed  and  much  has  been  said  about  the  superior 
bleaching  power  of  a  pound  of  chlorine  thus  prepared  over  the 
same  quantity  in  the  form  of  bleaching  powder  solution.  While 
these  claims  are  undoubtedly  made  in  good  faith  it  seems  prob- 
able that  many  are  based  on  incorrect  comparisons  since  tests 
of  efficiency  by  bleaching  for  a  given  time  and  determining  the 
residual  bleach  are  not  accurate  unless  exactly  the  same  colors 
are  produced.  Ahlin  l  states  that  it  is  not  true  that  active 
chlorine  produced  electrolytically  will  do  more  work  than  an 
equal  quantity  from  bleaching  powder,  and  Dorenfeldt 2  claims 
that  unless  brine  is  to  be  obtained  almost  free  of  cost  or  unless 
sodium  carbonate  is  worth  no  more  than  quick  lime  an  electri- 
cally prepared  bleach  liquor  (sodium  hypochlorite)  cannot  pos- 
sibly compete  with  bleach  obtained  from  an  electrical  chlorine- 
soda  process. 

There  have  been  proposed  from  time  to  time  other  bleach 
liquors  formed  by  the  addition  of  magnesium,  aluminum  or 

1  J.  Soc.  Chem.  Ind.,  1902,  718. 

2  Papier  Ztg.,  1903,  215. 


234  BLEACHING 

zinc  sulphate  to  a  bleaching  powder  solution.  These  have  the 
advantage  of  rapidity  of  action  and  except  for  their  high  cost 
would  be  useful  in  bleaching  paper  stock.  The  action  of  mag- 
nesium hypochlorite  is  purely  oxidizing  and  it  seems  to  have 
no  tendency  toward  the  formation  of  chlorinated  products,  while 
calcium  hypochlorite  shows  this  tendency  quite  strongly,  espe- 
cially when  acid  is  used.  Because  of  their  cost  these  solutions 
are  practically  never  used  except  in  isolated  cases  where  per- 
haps a  little  alum  is  added  to  the  beater  to  hasten  the  action. 

Principles  of  Bleaching.  The  general  principles  governing 
the  practical  application  of  the  bleaching  process  have  been 
carefully  worked  out  by  numerous  investigators,  who  have 
studied  among  other  factors  the  influence  of  concentration  of 
stock,  temperature  of  bleaching,  and  the  accelerating  effect  of 
acids,  air,  beating,  etc. 

The  concentration  of  the  stock  when  bleached  is  held  by 
Baker  and  Jennison  l  to  be  one  of  the  most  important  factors. 
This  is  doubtless  true  when  the  bleaching  is  conducted  by  add- 
ing an  excess  of  bleach  and  removing  the  unused  part  at  the 
end  of  a  certain  time.  Under  these  conditions  the  proportions 
of  stock  and  water  would  certainly  exert  a  considerable  influence 
on  the  color  produced  and  the  old  saying  "more  water,  more 
bleach"  would  hold  good.  If,  however,  a  definite  amount  of 
bleach  is  added  to  the  stock  and  the  action  allowed  to  continue 
until  the  bleach  is  exhausted  then  the  amount  of  water  used  is 
practically  without  effect  on  the  final  color  of  the  stock,  though 
it  has  a  great  influence  on  the  time  required  to  use  up  the  bleach. 
This  is  illustrated  by  tests  on  two  sulphite  fibres,  one  of  which 
required  5  per  cent  and  the  other  13  per  cent  of  bleach;  when 
these  were  bleached  at  a  concentration  of  one  part  of  fibre  in 
140  parts  of  water  they  required  21  to  22.6  hours  to  exhaust 
while  at  a  concentration  of  one  part  in  23  the  same  point  was 
reached  in  15  to  15.5  hours.  The  color  was,  however,  practi- 
cally the  same  in  both  cases. 

The  temperature  at  which  the  bleaching  is  conducted  has  a 

1  J.  Soc.  Chem.  Ind.,  1914,  284. 


PRINCIPLES   OF  BLEACHING  235 

very  pronounced  influence  on  the  results  obtained,  both  as  to 
color  produced  and  time  required  in  the  operation.  Cross  and 
Bevan  1  state  that  esparto  bleached  at  o°  to  4°  C.  uses  only 
80  per  cent  of  the  bleach  consumed  at  35°  C.  and  gives  an 
equal  color.  With  sulphite  spruce  and  soda  poplar  we  have 
found  that  to  exhaust  a  given  amount  of  bleach  at  40°  C.  re- 
quired eight  to  nine  times  as  long  as  it  did  at  65°  C.  This  extra 
speed  was  gained,  however,  at  the  expense  of  color,  for  the 
inferiority  of  the  samples  bleached  at  65°  C.  was  so  marked 
that  it  would  have  been  necessary  to  use  fully  5  to  10  per  cent 
more  bleach  in  order  to  bring  them  to  the  standard  .color. 
Simonsen 2  in  working  with  a  sulphate  pulp  found  that  7  per  cent 
of  bleach  was  sufficient  at  13°  C.  but  that  if  the  temperature 
were  raised  to  35°  C.  it  required  9  per  cent  of  bleach  to  give  the 
same  color.  Schwalbe  claims  that  temperatures  over  30°  C. 
are  to  be  avoided  as  bleach  is  lost  through  transformation  into 
chlorate;  this  is  quite  probably  one  of  the  chief  reasons  for  the 
poorer  color  obtained  at  higher  temperatures.  The  maximum 
temperature  which  it  is  safe  to  use  is  variously  stated  by  differ- 
ent authorities  at  from  68°  to  110°  F.  (20°  to  43°  C.).  No  hard 
and  fast  line  can  however  be  drawn  since  it  is  often  a  question 
of  adjusting  the  temperature  so  that  a  certain  output  may  be 
obtained  from  a  given  equipment.  In  such  cases  it  may  be 
for  a  time  better  policy  to  increase  the  temperature  rather  than 
replace  or  enlarge  the  apparatus  though  it  is  certainly  true  that 
if  the  temperature  rises  much  above  35°  to  40°  C.  an  appre- 
ciable portion  of  the  bleach  will  be  wasted. 

The  effect  of  temperature  on  the  time  required  for  bleaching  is 
well  illustrated  by  the  following  results  obtained  in  the  author's 
laboratory  on  three  different  kinds  of  fibre. 

1  J.  Soc.  Chem.  Ind.,  1890,  450. 

2  Paper  Trade  J.,  Feb.  12,  1914. 


236 


BLEACHING 


Fibre 

Bleach  used  for 
standard  color 

Hours  required  to  exhaust  bleach 

At  65°  C. 

At  40°  C. 

At  20°  C. 

Sulphite  

Percent 
13.0 
5-0 
ii.  5 

1-50 
1-25 
i-33 

12.0 

10.8 
13.0 

192 

E  B   sulphite 

Soda  poplar 

The  rate  at  which  bleach  is  consumed  is  also  shown  in  the 
following  table  which  contains  the  results  of  tests  by  the  author 
as  well  as  by  Sindall  and  Bacon.1  The  figures  show  the  per- 
centage of  the  added  bleach  which  was  consumed  in  the  times 
noted. 


Fibre 

Soda  poplar 

Soda  poplar 

Sodai 

Sulphite  ! 

Sulphite  i 

Bleach  added  
Temperature  C  

n-5 
40.0 

n-5 

12.0 

H-7 
18.0 

14 

18 

8 
18 

Time  in  hours 

Per  cent  of  bleach  consumed 

0-5 
i  .0 

.     i-5 

2  .O 

3-0 

4.0 
5.0 

6.0 
7-o 
8.0 
ii  .0 
71.0 

63.8 
70.0 

51-3 

55-3 

33/0 

44J.o 

5f  ° 
6fl.o 
7*.o 

8J>.o 

2O 

72.5 

30 

33 
43 
49 
56 

63 
70 

82.5 

71.7 

55 

78 
90 

73-i 
77-5 
96.7 

IOO.O 

1  The  Testing  of  Wood  Pulp. 

Weight  Lost  on  Bleaching.  The  loss  in  weight  which  all  fibre 
undergoes  on  bleaching,  because  of  the  oxidizing  and  dissolving 
power  of  the  bleach  solution,  is  in  accord  with  the  observed  facts 
regarding  the  influence  of  temperature.  Since  the  higher  tem- 
perature causes  quicker  action  and  gives  poorer  color  due  prob- 
ably to  chlorate  formation  it  would  be  expected  that  the  attack 
on  the  fibre  would  be  less  with  a  consequent  smaller  loss  in 

1  The  Testing  of  Wood  Pulp. 


WEIGHT  LOST  ON   BLEACHING 


237 


weight.  That  such  is  the  case  is  proved  by  the  following  results 
of  experiments  in  which  the  fibre  was  bleached  at  different  tem- 
peratures but  with  the  same  amount  of  bleach  until  the  latter  was 
completely  used  up. 


Fibre 

Percentage 
bleach  used 

Loss  in  weight  due  to  bleaching 

at  20°  C. 

at  40°  C. 

at  70°  C. 

Sulphite 

13.0 

5-o 
ii.  S 

Per  cent 
2.31 
1.89 
I.89 

Per  cent 

2.27 
1.66 

Per  cent 
1.97 
I.  II 
1.64 

E.  B.  sulphite  . 

Soda  poplar 

If  the  fibre  is  treated  with  an  excess  of  bleach,  which  is  not 
all  used  up  when  the  desired  color  is  reached,  then  an  increase  in 
temperature  would  be  expected  to  increase  the  loss  in  weight  and 
Simonsen  l  has  found  this  to  hold  true  in  the  case  of  a  sulphate 
pulp  which  lost  4.5  per  cent  of  its  weight  when  bleached  at  20°  C. 
and  6.1  per  cent  at  30°  C. 

The  amount  of  bleach  used  exerts  a  great  influence  on  the  loss 
in  weight  during  the  process  and  the  chemical  composition  of 
the  bleach  solution  probably  also  has  a  considerable  effect.  It  is 
hardly  to  be  expected  that  sodium,  magnesium  and  calcium 
hypochlorites  would  all  cause  the  same  loss  in  weight  and  the 
presence  of  alkali  or  acid  during  the  process  would  certainly  have 
an  influence.  With  calcium  hypochlorite  the  effect  of  increasing 
the  amount  of  bleach  used  is  illustrated  by  the  following  data: 


Fibre 

Per  cent  35%  bleaching 
powder  used 

Loss  in  weight  due 
to  bleaching 

Sulphite                    .        .      .          

13 

Per  cent 

2  .  27 

22 

1  .  Cl 

<  ( 

32 

5.06 

E.  B.  sulphite  

5 

1.66 

15 

3  -59 

«            « 

2< 

"?  .  72 

Soda  poplar                                 

II  .  < 

i  .94 

2O.  S 

3.69 

«          « 

30.5 

8.03 

1  Paper  Trade  J.,  Feb.  12,  19*14. 


238 


BLEACHING 


This  has  an  important  bearing  on  the  cost  per  ton  of  bleached 
fibre,  since  in  the  production  of  very  white  stock  not  only  ,is  the 
amount  of  bleach  increased,  but  the  loss  during  the  process  also 
rises  so  that  more  fibre  has  to  be  used  to  produce  a  ton  of  finished 
product.  In  commercial  fibres  the  loss  due  to  the  chemical 


.95 
.90 
.85 
.80 


FROM 

SINDALL  &  BACON 
"JESTING  OF  WOOD  PULP"  " 

P  120 

LOVIBOND  COLOR  READINGS 
Bleached  Hot Cold 


6   8 


10  12  14  16  18  20  22  24 
Bleach  used 

FIG.  34 


action  of  the  bleach  may  drop  as  low  as  i  per  cent  for  very  easy 
bleaching  stock  or  rise  as  high  as  5  per  cent  for  fibre  taking  20  to 
22  per  cent  of  bleach.  In  one  case  where  a  fibre  lost  12  per  cent 
of  its  weight  when  bleached  and  washed  it  was  discovered  that 
it  had  been  washed  in  the  blow  pits  with  sea  water  and  that 
about  one  half  of  this  loss  was  due  to  the  soluble  constitutents  left 
by  the  salt  water. 


USE  OF  BACKWATER  239 

The  rate  at  which  bleaching  eliminates  the  color  of  sulphite 
fibre  is  shown  graphically  in  Fig.  34,  which  is  plotted  from 
Sindall  &  Bacon's  book  on  the  Testing  of  Wood  Pulp.  The 
measurements  were  made  by  means  of  Lovibond's  tintometer  on 
samples  of  pulp  which  had  been  treated  with  progressively  larger 
amounts  of  bleach.  This  shows  very  plainly  the  comparatively 
rapid  disappearance  of  the  red  and  blue  and  explains  why 
bleached  pulp  generally  has  a  slightly  yellowish  tone. 

No  very  positive  statement  can  be  made  in  regard  to  the 
bleach  required  by  various  classes  of  paper  making  fibres  since 
it  depends  so  largely  on  the  way  the  unbleached  fibre  was-  pre- 
pared as  well  as  on  the  bleaching  method  employed  and  on  the 
color  obtained.  At  the  present  time  the  following  figures  are 
approximately  correct: 

Per  cent 

Rags ;..  .     2-5 

Sulphite  spruce 5-20 

Soda  fibres 8-15 

Use  of  Backwater.  The  character  of  the  water  used  in  break- 
ing up  the  pulp  preparatory  to  bleaching  has  an  appreciable 
influence  on  the  amount  of  bleach  required.  In  many  cases  it 
has  been  recommended,  and  has  been  the  practice,  to  use  the 
water  drained  from  the  bleached  pulp  to  make  up  another  charge 
for  bleaching.  This  is  not  to  be  recommended  since  it  is  attended 
with  an  increase  in  bleach  consumption  and  a  lowering  of  the 
color  of  the  pulp.  The  greater  bleach  consumption  is  caused  by 
the  organic  matter  in  solution  or  suspension,  which  continues 
to  use  up  bleach  when  further  portions  are  added.  In  a  number 
of  tests  by  the  author  this  "yellow  water"  removed  from  engines 
of  bleached  pulp  which  were  originally  furnished  entirely  with 
fresh  water  was  found  to  use  up  for  each  liter  of  water  from  0.94 
gram  of  35  per  cent  bleach  in  six  hours  to  1.53  grams  in  eighteen 
hours  at  35°  C.  Since  the  ratio  of  water  to  stock  was  30  :  i  in 
these  tests  it  is  evident  that  this  bleach  consumption  would  be 
equivalent  to  2.8  per  cent  to  4.6  per  cent  of  bleach  on  the  weight 
of  the  fibre.  Sindall  and  Bacon  1  found  that  at  32°  C.  the  bleach 

1  Testing  of  Wood  Pulp. 


240  BLEACHING 

used  up  by  this  residual  liquor  was  35.5  Ibs.  for  10,000  Ibs.  of 
water  while  at  49°  C.  it  amounted  to  112  Ibs.  These  quantities 
would  be  considerably  increased  if  the  water  were  used  over  and 
over,  thus  permitting  an  increase  in  the  concentration  of  the 
organic  matter.  The  use  of  uback"  or  " yellow"  water  for 
furnishing  the  unbleached  stock  is  therefore  to  be  recommended 
only  when  it  is  comparatively  rich  in  unused  bleach  and  when 
the  products  of  its  action  can  be  washed  out  before  the  final 
bleaching  is  commenced,  as  under  any  other  circumstances  its  use 
is  likely  to  cost  more  than  it  saves.  An  intermediate  washing  to 
remove  the  soluble  products  formed  by  bleaching  is  beneficial  as 
it  enables  a  better  color  to  be  produced  than  would  otherwise  be 
possible,  especially  with  hard-bleaching  pulps.  When  one-third 
of  the  bleach  is  used  up  before  such  washing  and  the  rest  after- 
ward it  has  been  found  in  actual  practice  that  about  90  Ibs.  of 
bleach  gave  the  same  results  as  100  Ibs.  when  all  is  added  at  once. 
The  bleaching  of  paper  stock  is  performed  in  engines,  chests 
or  drainers  according  to  the  equipment  available  or  the  personal 
preference  of  the  operator.  'Rag  stock  is  most  often  treated  with 
the  bleach  solution  in  the  engine  and  then  emptied  into  large 
tanks  or  chests  provided  with  false  bottoms.  In  these  the 
bleaching  is  completed  and  the  exhausted  bleach  solution  then 
allowed  to  run  away;  the  stock  may  then  be  treated  with  dilute 
sulphuric  acid  to  still  further  improve  the  color  and  finally 
washed  with  water.  The  process  may  be  hastened  by  heating 
the  contents  of  the  beater,  best  before  the  bleach  is  added,  since 
otherwise  it  is  likely  to  cause  local  overheating  with  Ibss  of 
bleach  and  formation  of  oxy cellulose.  Addition  of  acid  also 
hastens  the  bleaching  by  liberating  hypochlorous  acid  which  is 
more  vigorous  in  its  action  than  hypochlorite.  A  number  of  acids 
have  been  proposed  for  this  work,  from  sulphuric  to  acetic  or 
even  carbonic  which  it  has  been  proposed  to  lead  into  the  beating 
engine  just  under  the  roll.  The  known  accelerating  influence 
of  agitation  or  beating  is  due  doubtless  in  part  to  the  presence  of 
carbonic  acid  in  the  air.  Only  a  small  amount  of  acid  should  be 
used,  as  it  is  constantly  regenerated,  and  it  should  be  added  in  a 


SYSTEMS  OF  BLEACHING  241 

highly  dilute  condition  as  strong  acid  tends  to  liberate  chlorine 
and  cause  the  production  of  yellow  chlorinated  products.  Treat- 
ment with  acid  is  especially  useful  in  bleaching  shivey  flax  or 
linen  and  in  treating  rags  which  have  been  boiled  in  alkali  and 
hence  have  accumulated  basic  matters  which  might  be  injurious 
at  some  future  stage. 

Rags  may  also  be  bleached  before  reducing  to  half  stock  by 
washing  the  boiled  rags  and  treating  them  in  a  tumbler  with 
Weach  solution;  or  they  may  be  piled  up  in  chambers  and  the 
warm  bleach  circulated  through  them.  In  the  latter  case  they 
must  be  quickly  drenched  with  cold  water  and  transferred  to  the 
beaters  as  the  fibres  become  tender  if  allowed  to  stand  in  contact 
with  the  bleach.  Neither  of  these  methods  is  so  satisfactory  as 
that  of  bleaching  the  half  stock. 

Systems  of  Bleaching.  Bleaching  systems  in  general  may  be 
divided  into  two  classes,  one  a  rapid  bleach  in  which  an  excess  of 
fairly  strong  liquor  is  added  and  the  excess  removed  as  soon  as 
the  stock  has  reached  the  desired  color;  the  other  a  slower" 
process,  using  only  a  very  slight  excess  and  allowing  it  to  prac- 
tically exhaust.  The  rapid  bleach  necessitates  the  use  of  the 
excess  bleach  liquor  removed  from  the  bleached  stock,  which  has 
been  shown  to  be  uneconomical;  it  also  requires  more  careful 
control  since  the  higher  temperature  usually  maintained  and  the 
stronger  bleach  solutions  are  more  apt  to  cause  oxidation  of  the 
cellulose  and  a  consequent  weakening  of  the  fibre.  The  slower 
process  is  more  economical  of  bleach  but  requires  much  more 
space  for  a  given  output  and  in  the  choice  of  a  method  the  space 
available  for  the  plant  is  frequently  the  deciding  factor.  In  either 
method  the  amount  of  water  used  should  be  kept  as  low  as  pos- 
sible since  this  saves  both  bleach  and  time.  The  proportion  of 
water  to  fibre  will  necessarily  vary  with  the  type  of  apparatus 
employed  but  with  large  chests  furnished  with  good  agitators  it 
should  be  not  much  greater  than  30  to  i.  If  the  bleaching  is 
done  entirely  in  engines  somewhat  less  water  can  be  used,  while 
in  the  Belmer  bleaching  apparatus  the  stock  may  be  run  at  5^  to 
6|  per  cent  density. 


242  BLEACHING 

Recognition  of  the  advantage  of  using  as  little  water  as  pos- 
sible is  shown  in  Dobson's  bleaching  process  in  which  the  dry 
sheets  of  fibre  are  added  to  the  bleach  solution  in  a  drum-like 
vessel  which  is  then  closed  and  rotated  at  two  to  four  revolutions 
per  minute  for  about  three  hours,  when  the  bleaching  is  completed. 
The  claims  for  this  process  are  that  it  saves  time,  power  and 
floor  space  and  that  the  stock  needs  no  washing  or  draining  and 
is  ready  to  use  as  soon  as  the  bleaching  is  completed.  While  this 
process  might  be  applied  to  wood  pulp  it  is  obvious  that  rags 
which  have  been  cooked  with  lime  could  not  be  satisfactorily 
treated  by  it. 

The  bleaching  of  fibres  prepared  by  the  soda  process,  whether 
from  esparto,  straw  or  any  of  the  numerous  woods  now  used, 
follows  in  general  the  same  course  as  rag  stock.  Since  the  alka- 
line cooking  treatment  gives  a  well  reduced  fibre  with  a  tendency 
toward  an  alkaline  or  basic  condition  it  is  safe  to  use  a  little  acid 
in  the  process.  This  is  best  added  in  a  well  diluted  condition 
after  a  considerable  part  of  the  bleaching  has  taken  place  and 
even  then  it  must  be  used  with  care  as  these  celluloses  are  more 
easily  attacked  than  cotton  or  linen.  When  the  color  of  these 
fibres  has  reached  the  desired  point  the  bleach  residues  should 
be  quickly  removed  lest  the  stock  "go  back"  in  color;  this  is 
especially  likely  to  take  place  if  the  temperature  is  much  over 
30°  C.  The  removal  of  the  exhausted  bleach  may  be  readily 
accomplished  by  running  off  the  stock  on  some  form  of  wet 
machine  or  on  a  press-pate. 

The  treatment  of  sulphite  fibre  differs  slightly  from  that 
accorded  soda  fibre  since  it  has  already  a  tendency  toward  acidity 
because  of  its  method  of  preparation.  Also  it  is  usually  not  so 
thoroughly  freed  from  lignin  and  incrusting  matters  as  is  soda 
fibre  and  hence  is  more  liable  to  take  up  chlorine  with  the  forma- 
tion of  yellow  chlorinated  compounds.  As  acid  increases  this 
tendency  it  is  not  generally  used  with  sulphite  fibre,  though  it 
may  be  successfully  employed  by  adding  it  about  an  hour  after 
the  bleach,  washing  the  bleached  fibre,  which  is  frequently  orange 
colored,  and  rebleaching  with  ij  to  2  per  cent  of  bleach  followed 


JUTE  AND  MANILA  243 

by  a  little  acid.  This  treatment  is  unnecessarily  complicated 
as  most  sulphite  which  is  cooked  with  the  idea  of  making  into 
bleached  fibre  can  be  satisfactorily  treated  in  a  single  process. 
As  with  wood  pulp  prepared  by  the  soda  process  bleached  sulphite 
is  very  apt  to  "go  back"  in  color,  or  turn  yellowish,  if  it  stands 
in  contact  with  exhausted  bleach  liquors,  especially  at  elevated 
temperatures.  For  this  reason  it  is  quite  important  that  the 
temperature  be  kept  as  low  as  is  consistent  with  the  desired 
rapidity  of  bleaching  and  that  the  fibre  be  freed  from  bleach 
residues  as  soon  as  the  process  is  completed. 

In  handling  sulphite  fibre  it  is  frequently  observed  that  a  'rose 
color  develops  on  adding  bleach.  This  is  also  caused  by  ferric 
chloride,  potassium  ferricyanide,  mercuric  chloride,  potassium 
permanganate  and  potassium  bichromate.1  The  exact  reason 
for  this  phenomenon  is  not  known  but  as  the  color  produced  is 
roughly  proportional  to  the  amount  of  bleach  which  the  fibre 
requires  it  may  be  taken  as  giving  an  indication  of  the  bleaching 
properties  of  the  sample  in  question.  This  rose  color  is  only 
transitory,  as  it  disappears  very  quickly  as  the  bleaching  pro- 
ceeds, and  has  no  permanent  effect  on  the  color  of  the  fibre. 

Jute  and  manila  fibres  are  particularly  difficult  to  bleach  since, 
in  order  to  preserve  their  strength,  they  are  generally  only  lightly 
treated  with  milk  of  lime  and  hence  arrive  at  the  bleaching  process 
in  a  highly  lignified  condition.  For  this  reason,  and  because  the 
production  of  a  high  white  seriously  injures  the  strength  of  the 
stock,  they  are  seldom  bleached  beyond  a  good  cream  shade.  To 
hasten  the  action  4  to  5  per  cent  of  alum  is  sometimes  added  but 
if  the  stock  is  heated  this  is  particularly  likely  to  cause  the 
formation  of  yellow  chlorinated  compounds  which  defeat  the 
object  of  the  process.  The  bleaching  of  these  fibres  is  usually 
conducted  in  the  beater  but  in  some  cases  they  are  dumped  into 
drainers  in  which  the  last  part  of  the  bleaching  proceeds  slowly 
for  several  days.  The  chlorinated  compounds  mentioned,  when 
treated  with  a  solution  of  sodium  sulphite,  develop  a  strong 
magenta  color.  They  are  easily  soluble  in  alkalis  and  may  be 

1  J.  Soc.  Chem.  Ind.,  1896,  467'. 


244  BLEACHING 

removed  from  the  fibre,  by  treating  with  a  dilute  soda-ash 
solution. 

Ground  Wood.  The  treatment  of  ground  wood,  or  mechani- 
cal pulp,  so  as  to  improve  its  color,  is  a  problem  which  has  occu- 
pied the  attention  of  many  investigators.  Since  the  ground  wood 
contains  all  the  constituents  of  the  wood  itself,  except  a  very 
slight  amount  of  water-soluble  matter,  it  is  obvious  that  any 
treatment  with  hypochlorite  would  be  out  of  the  question,  since 
40  to  50  per  cent  of  the  weight  of  the  stock  would  have  to  be 
oxidized  and  dissolved  before  any  good  white  color  could  develop. 
The  first  effect  of  adding  hypochlorite  to  ground  wood  is  the 
production  of  a  red  or  brown  shade  which  persists  until  nearly  all 
of  the  incrusting  matter  has  been  destroyed. 

The  color  of  ground  wood  may  be  somewhat  improved  by 
treating  it  with  sulphurous  acid,  or  bisulphite  solution.  This  can- 
not be  considered  a  true  bleaching  process  as  the  coloring  matter 
is  not  destroyed  but  merely  masked  temporarily  and  the  color 
returns  on  exposure  to  the  air  for  some  time.  Considering  the 
results  obtained  sulphurous  acid  is  too  costly  and  the  reagent 
usually  employed  is  calcium  or  sodium  bisulphite.  One  method 
of  treatment  is  to  employ  about  2.5  per  cent  on  the  weight  of 
dry  fibre,  diluted  with  20  to  30  times  its  weight  of  water,  with 
which  solution  the  fibre  is  flooded  from  below  so  as  to  drive  out  the 
air.  After  allowing  to  stand  for  some  time  the  solution  is 
washed  out.  Another  procedure  is  to  spray  the  fibre  with  bisul- 
phite solution  as  it  is  taken  from  the  wet  machine  and  allow  the 
whitening  to  take  place  in  the  moist  laps.  In  this  case  no  final 
washing  is  given. 

Antichlors.  It  is  very  essential  that  the  bleached  stock  going 
to  the  beaters  should  contain  no  active  chlorine,  which  may 
readily  be  determined  by  means  of  iodide  of  starch  solution. 
This  may  be  prepared  by  boiling  up  a  little  starch  with  water  and 
adding  a  few  crystals  of  potassium  iodide.  A  little  of  this  test 
solution  sprinkled  on  the  pulp  will,  if  the  latter  contains  any 
bleach,  develop  a  blue  color  varying  from  a  faint  color  almost  to 
a  black  according  to  the  amount  of  bleach  present.  It  is  always 


ANTICHLORS  245 

best  to  test  the  stock  being  bleached  rather  than  the  water 
squeezed  from  it  since  if  much  bleach  is  present  in  the  latter  it 
may  destroy  the  blue,  while  if  the  bleach  is  nearly  exhausted  the 
liquor  sometimes  fails  to  give  a  test  though  the  stock  still  shows 
its  presence.  The  difficulties  encountered  and  the  time  required 
in  washing  out  the  last  traces  of  bleach  from  the  pulp  have  led 
to  the  use  of  various  chemicals  to  reduce  and  render  harmless  any 
which  may  remain  at  the  completion  of  bleaching.  Such  chemi- 
cals, from  the  nature  of  the  work  which  they  perform,  are  called 
antichlors. 

The  one  most  commonly  employed  is  sodium  thiosulphate, 
Na2S203  5  H2O,  or  " hyposulphite  of  soda"  as  it  is  generally 
called.  This  is  added  to  the  engine  as  a  dilute  solution  after  the 
stock  has  come  to  color.  It  acts  on  the  bleach  according  to  the 
following  reaction: 

2  CaO2Cl2  +  Na2S2O3  +  H20  =  2  CaSO4  +  2  NaCl  +  2  HC1, 

in  which  the  products  formed  are  calcium  sulphate,  or  "Pearl 
Filler,"  common  salt  and  hydrochloric  acid.  According  to 
Griffin  and  Little  1  if  the  solutions  employed  are  very  dilute  the 
decomposition  may  take  place  in  another  direction  as : 

Ca02Cl2  +  4  Na2S203  +  H2O  =  2  Na2S406  +  2  NaCl  +  2  NaOH 

+  CaO 

The  products  of  either  of  these  reactions  are  apt  to  exert  a  de- 
structive influence  on  the  machine  wires  and  their  presence  in  the 
paper  is  fully  as  serious  as  that  of  the  bleach  which  they  are 
intended  to  eliminate.  The  use  of  thiosulphate  is  therefore  not 
to  be  recommended. 

Safer  antichlors  to  use  are  sodium  sulphite,  Na2S03,  and 
calcium  sulphite,  CaSO3,  which  according  to  the  reaction, 

CaO2Cl2  +  2  Na2SO3  =  CaSO4  +  Na2SO4  +  2  NaCl 
or          CaO2Cl2  +  2  CaSO3  =  2  CaSO4  +  CaCl2, 

give  products  which  are  much  less  harmful  than  those  from 

1  Chemistry  of  Paper  Making. 


246  BLEACHING 

thiosulphate.  Because  of  the  slight  solubility  of  calcium  sulphite 
the  reaction  in  this  case  takes  place  rather  slowly  but  it  possesses 
the  advantage  that  any  excess  acts  as  a  filler  and  is  in  most 
cases  quite  harmless. 

Other  antichlors  which  have  been  proposed  are  the  ordinary 
sulphite  liquor  used  in  the  manufacture  of  wood  pulp;  the  mix- 
ture of  calcium  thiosulphate  and  polysulphide  prepared  by  boil- 
ing sulphur  with  milk  of  lime;  and  hydrogen  peroxide.  The 
first  of  these  is  a  rapid  and  efficient  antichlor  and  in  many  cases 
it  tends  to  brighten,  temporarily,  the  color  of  the  fibre.  It  must 
be  used  with  considerable  caution  as  any  excess  tends  to  set  up 
an  acid  condition  in  the  pulp  with  consequent  injury  to  wires, 
driers  and  even  the  paper  itself.  The  lime-sulphur  mixture  is 
probably  even  more  injurious,  since  a  considerable  amount  of 
free  sulphur  is  precipitated  on  the  fibres  during  the  reaction  and 
this,  because  of  its  finely  divided  condition,  is  gradually  oxidized 
to  free  sulphuric  acid,  which  renders  the  paper  brittle  by  reason 
of  the  formation  of  hydrocellulose.  The  free  sulphur  also  causes 
tendering  of  the  machine  wires  through  formation  of  metallic 
sulphides.  Hydrogen  peroxide  is  the  safest  of  all  the  antichlors 
since  it  forms  only  water  and  free  oxygen.  It  is,  however,  too 
expensive  for  commercial  use. 

There  are  times  when  the  use  of  an  antichlor  is  of  assistance  but 
the  regular  employment  of  such  an  agent  indicates  inefficient 
bleaching  methods  since  expense  is  being  incurred  in  destroying 
a  portion  of  the  bleach  which  should  be  employed  in  doing  useful 
work.  In  any  well  regulated  mill  it  should  be  possible  to  elimi- 
nate the  use  of  antichlors. 

Washing  Bleached  Pulp.  The  washing  of  bleached  pulp  to 
remove  chlorides  and  the  products  of  antichlor  action  is  generally 
considered  very  necessary  if  durable  paper  is  to  be  made  from  the 
stock.  While  this  is  probably  true  with  regard  to  excess  of 
antichlor  and  may  have  some  influence  in  the  case  of  the  chlorides 
formed  by  the  reduction  of  the  hypochlorite  yet  it  is  felt  that  for 
the  general  run  of  book  and  magazine  papers  too  much  stress  is 
laid  on  this  point.  This  opinion  is  based  on  experiments  carried 


PERMANGANATE   BLEACHING  247 

out  with  very  thoroughly  washed  soda  and  sulphite  pulps,  and 
with  part  of  the  same  lots  which  had  been  only  very  slightly 
washed  after  bleaching.  These  conditions  were  chosen  as  repre- 
senting the  best  and  worst  which  were  likely  to  occur  in  actual 
manufacturing  operations.  The  two  lots  were  beaten,  sized  and 
made  into  paper  in  the  same  way  and  pieces  of  the  paper  were 
then  exposed  to  sunlight  for  three  months  and  to  temperatures  of 
80°  to  90°  C.  for  eight  days.  Neither  of  these  tests  showed  greater 
discoloration  in  one  case  than  in  the  other  and  both  became 
brittle  and  unsized  to  about  the  same  extent.  The  conclusion 
that  slight  washing  is  not  likely  to  prove  injurious  to  the  dur- 
ability of  the  paper  is  put  forward  with  some  hesitation  as  it  runs 
counter  to  generally  accepted  theories  but  from  the  above 
experiments  no  other  conclusion  can  be  reached. 

Washing  will  however  improve  the  color  of  the  bleached  fibre 
by  removing  the  yellow,  soluble  products  of  the  bleaching  action, 
and  will,  in  large  measure,  prevent  the  brownish  discoloration 
which  is  sometimes  noticed  on  the  edges  of  wet  bleached  pulp 
after  storing  for  some  time.  According  to  Griffin  and  Little  this 
is  caused  by  the  concentration  of  calcium  chloride,  due  to  more 
rapid  evaporation  on  the  edges,  till  it  becomes  strong  enough  to 
act  on  the  fibre  and  form  colored  decomposition  products.  Our 
experiments  with  thoroughly  washed,  pure  filter  paper  and  a 
solution  of  chemically  pure  calcium  chloride  have  shown  that 
even  relatively  strong  solutions  fail  to  cause  any  discoloration 
even  under  very  severe  conditions  of  storage.  The  reason  for 
these  brown  edges  in  commercial  pulps  is  the  incomplete  removal 
of  the  soluble  organic  matter  which  is  brought  to  the  surface  and 
edges  of  the  pulp  by  capillary  action  and  there  concentrated  by 
evaporation  till  its  color  becomes  noticeable. 

Permanganate  Bleaching.  Permanganate  of  potash  has  often 
been  proposed  as  a  bleaching  agent  in  place  of  the  hypochlorites, 
and  all  sorts  of  claims  have  been  made  regarding  its  alleged 
superior  efficiency.  In  presence  of  acid  permanganate  reacts 
according  to  the  equation 

2  KMnO4  +  3  H2S04  =  K2S04  +  2  MnS04  +  3  H20  +5  O, 


248  BLEACHING 

while  in  neutral  solution  the  reaction  taking  place  is 

2  KMn04  +  H20  =  2  KOH  +  2  Mn02  +  36. 

Since  the  presence  of  acid  causes  too  powerful  an  attack  on  the 
fibre  it  is  necessary  to  bleach  in  neutral  or  slightly  alkaline 
solution. 

Permanganate  bleaching  is  extremely  rapid  and  there  is 
obviously  no  chance  for  the  formation  of  chlorinated  compounds. 
The  permanganate  should  be  added  to  the  stock  in  dilute  solution 
in  order  to  avoid  local  formation  of  oxycellulose.  When  the 
bleaching  has  been  completed  it  is  necessary  to  remove  the  brown 
manganese  peroxide  by  means  of  some  reducing  agent,  most 
conveniently  sulphur  dioxide,  or  an  acid  sulphite.  Beadle  con- 
siders the  sulphur  dioxide  to  act  as  follows: 

Mn02  +  S02  +  2  H20  =  Mn(OH)2  +  H2SO4, 
Mn(OH)2  +  H2S04  =  MnSO4  +  2  H2O. 

The  Mn(OH)2  being  white  is  practically  invisible  and  if  the  re- 
action goes  no  further  may  remain  in  the  pulp  and  cause  it  to  go 
back  in  color  by  absorbing  oxygen  and  turning  brown.  All 
manganese  peroxide  should  therefore  be  converted  to  the  sul- 
phate. As  all  the  alkali  formed  during  the  reduction  of  the 
permanganate  must  be  neutralized  before  the  manganese  per- 
oxide can  be  dissolved  it  is  evident  that  a  considerable  saving  of 
sulphur  dioxide  can  be  effected  by  using  some  cheaper  acid  for 
this  purpose. 

Beadle  found  by  experiments  on  rags  l  that  one  pound  of  per- 
manganate did  the  same  work  as  10  Ibs.  of  bleaching  powder  and 
concluded  that  the  oxygen  of  the  two  substances  acted  quite 
differently.  Our  own  experiments  with  sulphite  and  soda  fibres 
show  that  in  bleaching  effect  one  pound  of  potassium  per- 
manganate is  equivalent  to  1.854  Ibs.  of  35  per  cent  bleaching 
powder,  while  according  to  the  oxygen  evolved  one  pound  should 
equal  1.93  Ibs  of  bleach.  It  is  evident,  in  the  case  of  chemical 

1  Chapters  on  Paper  Making,  Vol.  II,  p.  117. 


EFFECT  OF  BLEACHING  ON  STRENGTH  OF  STOCK   249 

wood  fibres,  that  the  oxygen  evolved  by  the  two  substances  has 
the  same  bleaching  power. 

The  use  of  permanganate  for  conducting  the  entire  bleaching 
process  is  more  expensive  than  bleaching  by  hypochlorite  and  the 
necessity  of  acid  for  removing  the  manganese  peroxide  still  fur- 
ther increases  the  cost.  Even  when  the  greater  part  of  the 
bleaching  is  done  by  hypochlorite  and  the  final  treatment  only  is 
with  permanganate  the  increase  in  cost  is  out  of  all  proportion  to 
the  gain  in  whiteness.  For  these  reasons  permanganate  is  seldom 
employed  in  commercial  work. 

Sodium  peroxide  and  perborates,  persulphates,  etc.,  have,  also 
been  proposed  as  bleaching  agents  but  they  are  never  used  in 
this  country.  In  fact  von  Possanner  1  has  shown  that  sodium 
peroxide  is  of  little  value  for  bleaching  rag  stock,  since  even 
when  excessive  amounts  are  used  only  a  partial  bleaching  takes 
place.  Moreover,  if  employed  in  too  strong  solutions,  it  attacks 
the  fibre  and  forms  oxycellulose. 

Effect  of  Bleaching  on  Strength  of  Stock.  The  bleaching  of 
paper  stock  induces  in  it  a  two-fold  change  since  it  affects  both 
its  physical  and  chemical  properties.  Experiments  made  by 
Frohberg 2  led  him  to  conclude  that  bleaching  very  greatly 
reduced  the  folding  strength  in  comparison  with  that  of  paper 
made  from  the  unbleached  fibre.  In  nine  samples  of  sulphite 
which  he  tested  this  reduction  in  strength  varied  from  29.8  to 
62.7  per  cent  of  the  strength  shown  by  the  unbleached  fibre. 
The  breaking  length  was  affected  much  less  than  the  folding 
strength,  being  reduced  by  only  about  7  to  1 2  per  cent.  A  slight 
overbleaching  was  found  to  reduce  the  strength  and  durability 
of  the  paper  to  a  still  greater  extent. 

Our  own  very  carefully  conducted  experiments  entirely  con- 
tradict those  of  Frohberg.  Starting  with  the  unbleached  fibre, 
samples  were  beaten  and  made  into  hand  mould  sheets  under 
standard  conditions.  Portions  of  the  same  fibres  were  then 
bleached  with  two  different  amounts  of  bleach,  the  lowest  being 

1  Wochbl.  Papierfabr.,  44,  3161. 

2  Ibid,  44,  3599- 


250 


BLEACHING 


that  which  would  give  a  good  standard  white  shade,  and  the 
bleached  fibre  beaten  and  made  into  sheets  as  before.  The  air 
dry  sheets  were  then  subjected  to  folding  tests  on  the  Schopper 
folder,  and  to  bursting  tests  on  the  Ashcroft  tester.  The  results 
on  three  different  fibres  are  as  follows: 


Sulphite  No.  I 


Unbleached 


13  per  cent 
bleach 


22  per  cent 
bleach 


Folding  test 1.9  15.8 

Ashcroft  test 18.3  35.2 

Sulphite  No.  2 

Unbleached 

Folding  test 2.9  15.0 

Ashcroft  test 21.1  34.0 

Soda  poplar 

Unbleached        " 

Folding  test , 1.5  o.o 

Ashcroft  test 21.3  20 . 2 


11.9 
30.9 


4.4 
32.4 


o.o 
9.2 


With  the  sulphites  the  bleached  fibres  possess  greater  strength 
than  the  unbleached  even  when  bleached  to  an  extremely  white 
color,  while  the  strength  of  the  soda  fibre  is  reduced  by  bleach- 
ing. A  partial  bleaching  with  hypochlorite  followed  by  per- 
manganate was  found  in  every  case  to  give  a  stronger  fibre 
than  if  the  bleaching  were  carried  to  the  same  point  by  hypo- 
chlorite alone. 

In  this  connection  it  is  interesting  to  note  the  results  obtained 
by  O'Neill J  on  cotton  cloth  before  and  after  bleaching.  He 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  288. 


EFFECT   ON   CHEMICAL  PROPERTIES  251 

measured  the  weight  required  to  break  a  single  thread  with  the 
following  results: 


Before  bleaching 

After  bleaching 

No.  i  cloth, 

weft  threads  

Grains 
1714 

Grains 
278$ 

"    i      " 

warp                

3140 

2Q2O 

"      2         " 

3407 

3708 

«                 .i 

«           « 

3^12 

AQ2  ^ 

In  three  out  of  four  cases  there  is  a  distinct  increase  in  strength 
due  to  bleaching. 

In  our  opinion  it  is  safe  to  conclude  that  the  folding  and 
bursting  strength  of  sulphite  is  not  injured  by  bleaching  but 
that  with  soda  poplar  the  bleaching  process  does  occasion  a 
loss  in  strength. 

Effect  on  Chemical  Properties.  The  two  changes  in  the 
chemical  properties  of  the  fibre  which  are  most  likely  to  be 
caused  by  bleaching  are  the  formation  of  oxycellulose  and  chlori- 
nated cellulose.  If  acid  is  used  hydrocellulose  is  also  likely  to 
be  formed  locally. 

Griffin  and  Little  l  claim  to  have  found  between  5  and  6 
per  cent  of  chlorinated  cellulose  in  a  bleached  sulphite  pulp  of 
good  color,  while  Cross  and  Bevan  2  showed  that  during  the 
bleaching  of  wood  pulp  and  esparto  chlorine  combined  with  the 
residual  non-cellulose  constituents,  forming  chlorinated  com- 
pounds some  of  which  remain  fixed  on  the  fibres  after  washing. 
According  to  these  statements  the  presence  of  chlorine  in  a 
bleached  pulp  would  not  necessarily  indicate  insufficient  wash- 
ing. Contrary  to  these  opinions  Schwalbe 3  finds  that  when 
cellulose  is  bleached  by  hypochlorites',  whether  in  acid  or  alka- 
line solution,  the  amount  of  chlorine  which  combines  with  the 
substance  of  the  fibre  is  quite  negligible.  In  the  case  of  sul- 
phite cellulose  there  is,  however,  a  small  quantity  of  chlorine 

1  Chemistry  of  Paper  Making,  p.  286. 

2  J.  Soc.  Chem.  Ind.,  1890,  450. 

3  Chem.  Ztg.,  1907,  31,  940-941. 


252  BLEACHING 

absorbed.  Further  work  by  the  same  author  !  was  carried  out 
with  both  calcium  and  sodium  hypochlorite,  in  neutral  and 
acid  solutions  and  in  industrial  proportions  and  in  excess.  After 
bleaching  the  sulphite  cellulose  was  washed,  dried  and  carefully 
analyzed.  The  total  chlorine  in  the  bleached  pulps  from  these 
tests  varied  from  0.051  to  0.114  per  cent  and  of  this  0.047  to 
0.071  per  cent  was  present  in  combination  with  organic  matter, 
the  rest  being  combined  with  the  constituents  of  the  ash.  In 
spite  of  these  figures  Schwalbe  concludes  that  no  appreciable 
chlorination  of  the  pulp  takes  place  and  that  the  products  of 
bleaching  are  removed  during  the  process  of  washing. 

Besides  the  slight  chlorination  which  may  take  place  during 
bleaching  there  is  a  quite  appreciable  formation  of  oxycellulose. 
An  approximately  quantitative  estimation  of  the  amount  of 
hydro-  and  oxy-cellulose  formed  may  be  made  by  determining 
the  loss  in  weight  of  the  thoroughly  washed,  bleached  fibre 
when  boiled  in  0.25  per  cent  solution  of  caustic  soda,  or  by 
means  of  Schwalbe's  " copper  number"  method.2  This  latter 
method  is  a  determination  of  the  amount  of  copper  reduced  by 
the  fibre  on  boiling  with  Fehling  solution  under  carefully  regu- 
lated conditions  and  the  " copper  number"  is  the  number  of 
grams  of  copper  which  would  be  so  reduced  by  100  grams  of 
absolutely  dry  fibre. 

Using  the  two  methods  to  study  the  effect  of  various  bleach- 
ing conditions  the  following  data  were  collected  from  experi- 
ments on  two  samples  of  sulphite  and  one  of  soda.  All  figures 
are  based  on  the  materials  as  weighed  out  for  analysis  and  are 
not  reduced  to  a  common  basis. 

These  figures  demonstrate  that  the  more  bleach  used,  and 
hence  the  whiter  the  product,  the  greater  will  be  the  attack  on 
the  cellulose  itself.  They  also  show  clearly  that  permanganate 
causes  much  less  oxycellulose  formation  than  an  equivalent 
quantity  of  hypochlorite. 

1  Z.  angew.  Chem.,  1908,  21,  302-303. 

2  Z.  angew.  Chem.,  23,  924  (1910),  or  Chemie.  der  Cellulose,  p.  625. 


EFFECT  ON  CHEMICAL  PROPERTIES 


253 


Copper  number 

Loss  in  weight  on 
boiling  with  0.25 
per  cent  NaOH 

Sulphite  No 

.  i      unbleached  

2.56 

Per  cent 
II.5 

«<          « 

i      13      per  cent  bleach 

2   8l 

IO.Q 

«          « 

I        22                                      " 

2      Cl 

14.2 

«          «< 

I         32                 " 

7    I2, 

21  .7 

«          « 

Sulphite  No 

1    1*5.4        "        KMnOi'  .'.'.' 
2    unbleached  

}            4-13 
3.18 

15-3 
13  .O 

<<          « 

2    5  per  cent  bleach  

c 
2  .36 

IO.2 

«          « 

2  I<            "                  "... 

4-99 

17-4 

«          « 

2   21 

7  QQ 

2^.2 

Soda  poplar 

unbleached  

0.72 

0          4 

i-5 

it         « 
«          « 

ii  .5  per  cent  bleach  

20.5                             
20  ? 

3-04 
6.70 
10.  30 

10.5 

22.  0 

27.7 

r  ii  5 

1 

(   5  4        "        KMnO4  

4.20 

13-4 

By  this  same  method  of  study  Schwalbe  has  proved  l  that 
acid  bleaching  attacks  cellulose  more  than  alkaline,  both  in  hot 
and  cold  bleaching.  His  results  are: 


Copper  number 


Alkaline  bleach 

Acid  bleach 

Hot.  . 

2.86 

3-54 

Cold 

2   77 

4.23 

In  some  commercial  sulphites,  particularly  those  which  are 
slightly  undercooked  and  hence  hard  to  bleach,  it  is  difficult 
to  obtain  the  pure  white  which  is  desired  and  occasionally  the 
attempt  is  made  to  mask  the  remaining  yellow  color  by  the 
careful  use  of  blue.  Any  such  improvement  in  color  serves 
only  to  disguise  the  true  value  of  the  pulp  and  the  practice 
should  be  strongly  discouraged.  The  addition  of  blue  can  im- 
prove the  color  only  when  the  bleached  pulp  has  a  yellow  tint 


1  Wochbl.  Papierfabr.,  39,  2273. 


254  BLEACHING 

as  well-bleached  pulps  which  have  already  reached  a  good  de- 
gree of  whiteness  are  made  distinctly  gray  by  the  addition  of 
blue  and  pink.  If  any  considerable  amount  of  blue  has  been 
added  to  the  pulp  it  is  generally  quite  noticeable,  especially  on 
looking  through  the  suspected  sample.  When  a  smaller  amount 
has  been  used  its  presence  may  usually  be  detected  by  rolling 
the  sample  into  a  tube  and  looking  through  it.  in  which  case 
the  multiple  reflections  of  the  light  before  reaching  the  eye 
intensify  the  color. 

There  is  a  tendency  with  all  bleached  fibres  to  change  some- 
what in  color  when  kept  for  any  length  of  time  and  while  the 
alteration  which  takes  place  is  slight  and  the  chemistry  of  the 
process  obscure,  yet  experiments  have  brought  out  some  inter- 
esting facts.  It  has  been  shown  that  bleached  sulphite  which 
has  been  stored  in  well-seasoned  hard-wood  or  tin  receptacles 
hardly  changes  in  color  within  six  months,  while  similar  samples 
stored  in  pine-wood  boxes  became  somewhat  yellower  in  the 
same  time.  Direct  exposure  to  sunlight  gives  sulphite  a  red- 
dish tone  while  if  part  of  the  sheets  are  protected  from  the  light 
by  black  paper  the  portions  thus  protected  become  much  yel- 
lower than  the  fibre  before  exposure.  Soda  fibre  is  more  sus- 
ceptible to  these  changes  than  sulphite  and  the  more  highly 
bleached  the  fibre  the  more  rapidly  it  appears  to  deteriorate. 
These  facts  have  a  distinct  bearing  on  the  preservation  of  stand- 
ard samples  of  bleached  pulps  and  indicate  the  precautions 
which  should  be  taken  in  studying  the  changes  which  take  place 
on  exposure  to  light. 

Testing  Bleaching  Powder.  In  testing  bleaching  powder  the 
first  requisite  is  a  fair  sample.  This  should  be  obtained  by 
boring  a  hole  through  the  side  of  the  cask  midway  between  the 
ends  or  through  the  head  near  the  centre,  and  inserting  a  sampler 
two  or  three  inches  into  the  bleach.  The  first  sample  should 
be  rejected  and  the  sampler  again  inserted  as  far  as  it  will  go, 
the  sample  thus  obtained  should  be  placed  at  once  in  a  glass 
fruit  jar  which  must  be  closed  until  the  next  cask  is  sampled. 
Every  third  or  fourth  package  should  be  sampled,  according  to 


TESTING  BLEACHING  POWDER  255 

the  size  of  the  shipment,  but  in  no  case  should  less  than  20 
per  cent  of  the  total  packages  be  opened. 

The  sample  should  be  well  and  quickly  mixed,  breaking  up 
any  lumps  with  a  stout  glass  rod,  and  10  grams  weighed  out, 
put  in  a  porcelain  mortar,  a  little  water  added  and  the  mixture 
rubbed  to  a  smooth  cream.  More  water  is  mixed  in  with  the 
pestle,  allowed  to  settle  a  little  while  and  then  poured  off  into  a 
liter  flask;  the  sediment  is  again  rubbed  up  with  water,  and 
the  process  repeated  till  the  whole  of  the  sample  has  been  trans- 
ferred to  the  flask  and  the  mortar  washed  quite  clean.  The 
flask  is  then  filled  to  the  mark,  thoroughly  shaken  and  56  c.c. 
at  once  removed  with  a  pipette  and  placed  in  a  beaker  or  cup. 

N 
To  this  solution  is  then  added  standard  —  arsenite  solution 

5 

until  a  drop  of  the  mixture  taken  out  with  a  glass  rod  and 
brought  in  contact  with  potassium  iodide  starch  solution  gives 
no  blue  color.  The  percentage  of  available  chlorine  may  then 
be  calculated  by  the  formula: 


cubic  centimeters  arsenite  solution  X  0.7092  X  20 
grams  bleaching  powder  taken 


per  cent 
available  Cl. 


The  analysis  may  also  be  carried  out  by  adding  an  excess  of 
arsenite  solution  to  the  bleach  and  titrating  the  excess  with 
standard  iodine  solution.  This  involves  the  use  of  another 
standard  solution  and  is  no  more  accurate  than  Penot's  method 
as  outlined  above. 

N 
The  standard  —  arsenite  solution  is  prepared  by  dissolving 

exactly  9.9  grams  of  the  purest,  powdered,  sublimed,  arsenious 
oxide  in  about  500  c.c.  distilled  water  in  which  40  grams  pure 
sodium  carbonate  have  been  dissolved.  In  order  to  accomplish 
this  it  is  necessary  to  heat  the  mixture  on  the  steam  bath.  In 
spite  of  using  the  highest  purity  chemicals  it  is  generally  neces- 
sary to  filter  the  solution,  which  is  afterwards  cooled  and  made 
up  to  a  liter.  The  strength  of  this  solution  is  best  ascertained 
by  titration  against  a  standard  iodine  solution. 


256  .'         BLEACHING 

The  starch-paste  indicator  may  be  made  according  to  the  fol- 
lowing formula  which  has  been  found  to  give  excellent  results. 
Mix  three  grams  of  potato  or  arrow  root  starch  to  a  thin  cream 
with  cold  water  and  pour  into  250  c.c.  of  vigorously  boiling 
water.  Cool,  add  a  solution  of  i  gram  potassium  iodide  and 
i  gram  crystallized  sodium  carbonate  and  dilute  to  500  c.c. 


CHAPTER  IX 
SIZING 

For  some  purposes  papers  are  required  to  be  porous  and 
absorbent,  in  order  to  allow  the  passage  of  fluids,  as  in  filter 
paper,  or  their  rapid  absorption  as  in  blotting  paper,  but  for 
most  applications,  which  imply  the  use  of  ink  of  some  kind, 
it  is  desirable  that  they  be  more  or  less  non-absorbent.  This 
is  particularly  essential  in  the  case  of  writing  papers  which 
come  in  contact  with  very  fluid  inks,  and  in  papers  which  are 
to  be  used  for  coating,  and  it  is  even  considered  of  importance 
in  printing  papers  though  the  nature  of  printing  ink  is  such 
that  good  letter-press  work  can  be  done  on  an  unsized  or  water- 
leaf  paper.  Since  the  absorbent  power  of  paper  depends  on 
the  capillary  action  of  the  fibre  surfaces  and  on  the  spaces 
within  and  between  the  fibres,  it  is  necessary,  in  order  to  make 
the  paper  non-absorbent,  to  coat  the  fibres  with  some  substance 
which  will  offer  resistance  to  the  passage  of  ink.  This  object  is 
accomplished  by  various  methods  of  sizing.  ,\ 
!  The  degree  of  sizing  and  the  nature  of  the  agents  employed 
depend  upon  the  use  to  which  the  paper  is  to  be  put.  For 
news  paper,  on  which  the  ink  must  dry  very  rapidly  and  almost 
wholly  by  absorption,  the  sizing  must  be  slight  so  that  capillary 
action  may  not  be  prevented;  for  book  papers  the  sizing  is 
usually  harder  than  for  news,  not  because  the  inks  used  are 
more  easily  absorbed,  but  because  the  sizing  makes  the  paper 
more  satisfactory  for  general  service;  for  lithograph  papers  the 
sizing  must  be  still  harder  because  the  paper  becomes  moistened 
during  printing,  while  for  writing  papers  on  which  very  fluid  inks 
are  used  the  sizing  must  be  particularly  hard  so  that  the  ink 
may  not  spread  and  the  lines  become  blurred7~lln  the  days 

257 


258  SIZING 

of  hand-made  papers  the  sheets  were  sized  by  dipping  them 
into  a  tub  of  gelatine  solution  and  the  process  was  known  either 
as  tub  or  animal  sizing  from  the  nature  of  this  operation.  A 
modified  form  of  this  process  is  still  employed  and  as  it  con- 
sists essentially  of  the  deposition  of  a  layer  of  the  sizing  mate- 
rial on  the  surface  of  the  paper  it  might  well  be  spoken  of  as 
surface  sizing. 

This  method  of  sizing  is  too  slow  and  expensive  for  the  great 
bulk  of  modern  printing  papers  and  for  such  other  processes 
have  been  devised.  Most  of  these  depend  upon  the  precipita- 
tion on  the  fibres  of  some  material  which  on  drying  renders  the 
sheet  either  repellent  or  resistant  to  moisture  and  as  this  opera- 
tion generally  takes  place  in  the  beating  engine  it  is  usually 
cajled  engine  sizing. 

L  Surf  ace  Sizing.  Numerous  materials  have  been  proposed 
from  time  to  time  for  use  in  surface  sizing  but  practically  none 
are  used  in  appreciable  quantities  except  glue  and  starch  and  of 
these  much  more  of  the  former  is  consumed  than  of  the  latter. 
For  high-gradepapers  the  best  of  glue,  known  as  gelatine, 
should  be  used.  [  These  two  terms  are  often  indiscriminately 
applied,  which  is  quite  natural  since  .gelatine  may  be  considered 
as  a  highly  purified  glue  which  has  been  made  with  especial  care. 

Pure  gelatine  is  a  colorless,  odorless,  nearly  transparent,  nitroge- 
nous substance  which  is  insoluble  in  cold  water  but  which 
swells  and  absorbs  three  or  four  times  its  weight  when  soaked 
in  it.  In  hot  water  it  dissolves  readily  and  a  strong  solution 
sets  to  a  firm  jelly  on  cooling,  even  as  little  as  i  per  cent  giving 
a  gelatinous  mass.  [The  purest  commercial  form  of  gelatin  is 
isinglass  which  is  made  from  the  swimming  bladders  of  various 
kinds  of  fish;  below  this  in  quality  are  the  different  grades  of 
hide  glue  and  still  further  down  the  scale  are  the  bone  glues. 
Many  of  the  glues  are  excluded  from  sizing  work  because  of 
their  poor  color  and  others  because  of  their  low  gelatinizing 
power^ 

In  most  instances  it  is  better  for  the  paper  maker  to  purchase 
a  gelatine  or  glue  of  standard  quality  than  it  is  for  him  to  try 


SURFACE   SIZING  259 

and  make  it.  He  is  likely  to  get  a  more  uniform  product  and 
moreover  it  is  claimed  that  size  made  from  air-dried  glue  is 
superior  to  that  made  from  the  original  jelly.  The  gelatine 
which  gives  the  firmest  jelly  is  considered  the  best  sizing  agent 
and  as  a  general  rule  the  higher  priced  gelatines  will  be  found 
the  cheapest  in  the  end  because  of  their  greater  efficiency.  A 
gelatine  of  high  gelatinizing  power  gives  a  solution  with  a  low 
specific  gravity,  while  with  low-grade  glues  the  reverse  is 
true. 

TThe  strength  of  solution  used  in  sizing  generally  varies  be- 
tween 4  and  7  per  cent  and  the  temperature  at  which  it  is  applied 
may  range  from  85°  to  i2o°F.  To  this  solution  alum  is  fre- 
quently added  to  act  as  a  preservative  and  aid  in  preventing 
spoiling  of  the  sized  paper  .in  damp  auTJ  On  adding  the  alum 
the  glue  solution  thickens,  and  as  the  amount  is  increased  it 
may  almost  form  a  jelly;  strangely  enough,  however,  if  still 
more  alum  is  added  the  solution  becomes  thin  again  and  may 
even  be  more  fluid  than  the  original  solution.  This  property 
offers  a  convenient  means  of  controlling  the  penetration  of  the 
paper  by  the  size,  since  this  depends  in  part  on  the  fluidity  of 
the  solution.  The  influence  of  alum  added  to  the  gelatin  is 
shown  in  the  following  table  l  which  gives  the  percentage  of 
gelatine,  based  on  the  original  dry  paper,  absorbed  from  a  5  per 
cent  solution  by  papers  sized  with  different  amount  of  rosin. 

Percentage  of  rosin  size o.  o        0.5       i.o       1.5       2.0       2.5 

Gelatine  absorbed,  no  alum  used 12.1       10.9      8.9      8.0      7.2      6.5 

Gelatine  absorbed,  8  per  cent  alum  used     10.  2         9.  i       7.5       6.  5       5.7       5.2 

LAnother  substance  occasionally  added  to  the  size  solution  is 
soap,  which  is  claimed  to  have  a  certain  lubricating  effect  on 
the  fibres,  to  improve  the  opacity  and  to  disguise  the  color 
of  poor  glue.  The  soap  is  dissolved  to  a  clear  solution  in  water 
and  added  to  the  glue  solution  before  the  alum,  the  addition  of 
which  decomposes  the  soap.  J  Not  every  kind  of  soap  is  suitable 
for  this  work  as  its  nature  must  be  such  that  the  addition  of 

1  Cyster:  Paper,  May,  1915,  p.  18,  from  World's  Paper  Trade  Review. 


260  SIZING 

alum  produces  a  fine  emulsion  rather  than  a  curdled  mass  of 
fatty  acids. 

LThe  mechanical  operations  involved  in  surface  sizing  sheets 
of  paper  are  of  a  comparatively  simple  nature;  the  sheets  are 
suspended  in  a  vat  of  the  hot  size  till  the  air  is  expelled,  the 
excess  of  size  is  removed  by  pressing  and  the  sheets  are  hung 
up  to  dry.  The  immersion  of  the  sheets  is  sometimes  accom- 
plished by  feeding  them  between  endless  felts  into  the  size 
solution  in  a  vat  which  must  be  long  enough  to  give  time  for 
the  air  to  escape  from  the  paper ."7  As  applied  to  waterleaf 
papers  this  process  is  expensive  because  of  the  cost  of  handling 
single  sheets  and  because  of  the  large  amount  of  size  absorbed. 
This  latter  depends  on  the  viscosity,  temperature,  and  strength 
of  the  glue  solution  and  upon  the  condition  of  the  paper.  Free 
stuff  absorbs  more  glue  than  wet  beaten  stock,  while  bone  dry 
paper  absorbs  it  less  rapidly  than  that  with  an  appreciable 
amount  of  moisture. 

/Jn  this  country  practically  all  surface  sized  paper  is  made  as 
a  part  of  the  paper  machine  operation  by  leading  the  web  of 
paper  through  a  trough  filled  with  the  size  which  is  maintained 
at  the  desired  temperature  by  continual  circulation  to  and  from 
the  supply  tank.  This  method  enables  the  paper  to  be  engine 
sized  with  rosin  and  partially  dried  by  passing  over  a  few  cylin- 
ders before  reaching  the  size  trough  so  that  the  amount  of  glue 
absorbed  is  materially  reduced.^  If,  after  removing  the  excess 
of  size  by  squeeze  rolls,  the  paper  is  reeled  up  and  allowed  to 
season  a  short  time  before  drying  the  sizing  is  improved,  but 
in  many  cases  it  passes  directly  from  the  squeeze  rolls  to  the 
driers  which  are  skeleton  drums  around  which  the  paper  passes 
and  within  which  are  fans  to  keep  up  a  circulation  of  air. 

\The  drying  of  animal  sized  papers  is  a  matter  of  particular 
importance  since  the  quality  of  the  product  depends  largely  on 
this  operation^/  It  is  desirable  to  dry  slowly,  without  agitation 
and  at  a  temperature  below  that  required  to  liquefy  the  jelly]  so 
that  the  problem  is  really  that  of  drying  a  jelly  rather  than  a 
solution.  Loft  drying  is  the  best  but  the  slowest  and  most 


SURFACE   SIZING  261 

expensive,  the  festoon  arrangement  used  in  drying  coated  papers 
gives  fair  results  but  is  not  perfect,  while  if  the  paper  is  dried  on 
a  steam  cylinder  the  glue  has  little  sizing  power  since  individual 
fibres  only  -are  coated  and  the v  interstices  are  vacant.  /Papers 
dried  on  the  skeleton  drums  are  subjected  to  so  much  vibration 
from  the  fans  that  the  surface  tends  to  crack  and  the  product  is 
therefore  inferior  to  loft  dried  paper.  If,  after  drying,  the  sizing 
is  found  to  be  defective  it  may  sometimes  be  improved  by 
wetting  and  again  drying.  The  temperature  of  drying  depends 
in  part  on  the  atmospheric  humidity.  If  this  is  low  the  drying 
takes  place  rapidly  and  a  correspondingly  low  temperature  may 
be  employed  but  if  the  humidity  is  high  the  temperature  must 
be  raised  to  permit  evaporation  to  take  place.  The  upper  limit 
is  set  by  the  liquefaction  of  the  sizing,  which  in  general  may  be 
said  to  take  place  at  lower  temperatures  with  the  poorer  grades 
ofglue  than  it  does  with  gelatines. 

LJSurface  sizing  makes  paper  stronger  and  firmer  and  gives  a 
better  surface  for  writing  than  does  engine  sizing.  Its  effect  is 
reduced  by  the  subsequent  operations  of  calendering,  rolling  or 
plate  glazing  which  explains  the  fact  that  papers  with  a  rough 
surface  are  more  easily  hard  sized  than  those  which  are  highly 
glazed. 

The  operation  of  surface  sizing  with  glue,  while  apparently 
a  simple  one,  is  in  reality  one  of  the  most  difficult  and  uncertain 
of  all  those  carried  out  by  the  paper  maker,  since  the  gelatine  is 
influenced  to  so  great  an  extent  by  atmospheric  conditions  and 
its  absorption  is  so  dependent  on  the  physical  and  chemical  con- 
ditions of  the  paper  employed^/7 

The  tests  to  which  glue  or  gelatine  for  surface  sizing  should  be 
subjected  are  those  for  grease,  acidity,  ash,  added  alum  and  firm- 
ness of  jelly.  The  methods  for  the  first  two  are  given  in  the 
chapter  on  coated  papers.  The  ash  may  be  determined  by 
burning  out  a  weighed  sample  in  a  porcelain  crucible  and  weigh- 
ing the  residue  which  should  then  be  examined  for  alumina  by 
the  usual  qualitative  procedure.  The  presence  of  the  latter 
indicates  that  the  jelly  test  may  not  be  a  just  criterion  of  the 


262  SIZING 

sizing  value  of  the  glue  since  it  is  probable  that  alum  has  been 
added  to  increase  the  thickness  of  its  solution.  The  jelly  strength 
may  be  found  by  comparing  that  formed  from  a  definite  strength 
of  solution  with  that  from  standard  samples  similarly  treated. 
It  may  be  determined  numerically  by  preparing  jellies  from  the 
same  strength  of  solution  and  noting  the  time  required  for  a 
definite  weight  to  penetrate  the  jelly  a  given  distance  or  by 
determining  the  force  required  to  remove  a  plunger  round  which 
the  jelly  has  been  formed. 

L$>tarch.     This  material  is  used  in  sizing  both  as  a  substitute 
for  animal  size  and  in  the  engines.7 

For  surface  sizing  the  solutions  of  the  untreated  starches  are 
too  thick  to  be  applied  in  the  ordinary  manner  or  if  they  are 
reduced  to  the  proper  consistency  so  much  water  has  to  be  used 
that  enough  starch  to  be  effective  is  not  present.  For  this 
reason  the  (chemically  treated,  or  so-called  modified,  starches  are 
used  for  this  work.  These  are  dissolved  by  boiling  in  water  and 
are  applied,  either  with  or  without  the  addition  of  soap,  wax  or 
other  chemicals,  in  much  the  same  manner  as  animal  size.  Used 
in  this  way  they  give  a  firmness  and  rattle  to  the  paper  but  they 
are  not  so  effectual  in  sizing  against  writing  ink  as  are  animal 
sizes.  ~This  is  probably  due  in  part  to  the  hygroscopic  nature  of 
starch  and  partly  to  the  fact  that  it  does  not  form  a  jelly  on  cooling 
and  hence  does  not  fill  up  the  spaces  between  the  fibres  as  does 
gelatine. 

For  use  in  the  beating  engines  various  kinds  of  starch  are 
available  but  the  one  used  is  generally  that  which  can  be  obtained 
most  cheaply,  due  regard  being  paid  to  quality.  For  this  reason 
corn  starch  is  used  almost  entirely  in  this  country  while  in 
Europe  potato  starch  is  largely  employed.  1jhe  starch  is  added 
to  the  engine  either  in  the  raw  condition  or  after  boiling  with 
water  to  form  a  paste.  /The  retention  of  the  raw  starch  is  un- 
doubtedly greater  than  that  of  the  boiled  but  its  effect  in  harden- 
ing the  paper  may  not  be  any  greater  since  in  order  to  accomplish 
this  it  must  be  gelatinized  during  the  passage  of  the  paper  over 
the  driers.  Examination  of  papers  made  from  stock  containing 


STARCH  263 

raw  starch  shows  that  many  granules  are  not  even  swollen  and 
such  can  have  little  value  except  as  a  filler. 

Because  of  the  difficulty  of  accurately  determining  starch  in  the 
presence  of  cellulose  little  definite  information  is  available  as 
to  the  percentage  retained.  It  has  been  shown  by  Lutz  1  that 
the  retention  varies  with  the  kind  of  starch  and  the  condition 
when  added.  With  hand-made  papers  prepared  from  stock  to 
which  10  per  cent  of  starch  had  been  added  he  obtained  the 
following  retentions: 


Kind  of  starch 

Retention  when  added          » 

Raw 

Boiled 

Potato  

Per  cent 

73-6 
71.7 
53-4 

Per  cent 
46.2 
58.3 
58.9 

Wheat  

Rice  

It  is  interesting  to  note  that  with  raw  starch  the  larger  grains 
are  retained  better  while  if  the  starch  is  boiled  the  better  reten- 
tion occurs  with  those  starches  which  give  the  stiffest  pastes. 
It  is  very  doubtful  if  such  high  retentions  as  the  above  can  be 
expected  in  the  case  of  machine-made  papers  where  the  chances 
for  loss  are  so  much  greater. 

(Starch  used  in  the  beating  engine  hardens  the  paper,  prevents 
dusting,  increases  the  strength  and  tends  to  keep  down  the  fuzz 
caused  by  insufficiently  beaten  stock./  It  probably  increases  the 
retention  of  filler  very  slightly  but  the  gain  in  loading  is  not 
great  enough  to  pay  for  the  starch  required,  (jt  cannot  be  con- 
sidered a  sizing  agent  in  the  same  sense  as  rosin  for  it  imparts  no 
waterproof  qualities. 

There  has  recently  been  exploited  a  so-called  sizing  process, 
using  starch  and  silicate  of  soda,  in  which  the  starch  granules  are 
swollen  by  heat  in  the  presence  of  the  silicate  solution.  The 
theory  is  that  the  silicate  penetrates  the  starch  granules  as  they 
swell  and  that  when  alum  is  added  the  silicate  is  thrown  down 

1  Papier  Ztg.,  1908,  pp.  1098  and  1142. 


264  SIZING 

and  carries  the  starch,  with  it.  This  process  was  claimed  to 
retain  all  the  filler,  increase  the  strength  of  the  paper,  and  give 
a  better  printing  sheet.  Practical  trials  on  a  large  scale  have 
shown  that  it  does  not  appreciably  increase  the  retention  of 
filler  but  that  it  does  give  a  stronger  paper.  In  one  run,  that 
part  sized  with  silicate-starch  was  15  to  18  per  cent  stronger  than 
that  in  which  no  starch  or  silicate  was  used,  while  in  another 
thinner  order  the  gain  in  strength  was  38  to  46  per  cent.  On  the 
whole  the  results  by  this  process  appear  to  be  in  no  way  superior 
to  those  obtained  by  adding  starch  and  silicate  separately  to  the 
engine. 

Rosin.  This  material  is  used  in  engine  sizing  to  a  greater 
extent  than  all  other  sizing  agents  together.  It  is  obtained  as  a 
residue  after  distilling  off  the  volatile  portion  from  crude  turpen- 
tine which  is  obtained  in  this  country  largely  from  the  longleaf 
pine.  "7Since  the  crude  turpentine  contains  sand,  bark,  chips  and 
other^dirt  these  materials  are  always  to  be  met  with  in  commer- 
cial rosin.  The  point  to  which  the  distillation  of  the  turpentine 
has  been  carried  influences  the  color  of  the  rosin,  the  higher  the 
temperature  the  darker  being  the  product.  It  also,  to  a  certain 
extent,  determines  the  commercial  grading  of  the  rosin  since  the 
grade  depends  on  the  color.  Letters  are  used  to  denote  the 
quality  of  the  rosin,  A  being  nearly  black,  while  the  lightest 
colored,  W.W.,  or  water  white,  is  pale  yellow.  The  medium 
grades,  F  and  G,  are  those  most  commonly  employed  in  paper 
sizing,  and  are  considered  to  give  better  results  than  those  of 
lighter  color  since  the  higher  temperature  of  distillation  insures 
the  presence  of  less  pitch. 

JRosin,  or  colophony,  is  3,  transparent  or  translucent  resin, 
nearly  tasteless,  very  brittle^nd  showing  a  conchoidal  fracture. 
Its  specific  gravity  is  1.07  to  1.08.  It  softens  at  70°  to  80°  C., 
becomes  semi-fluid  in  boiling  water  and  melts  completely  at  a 
somewhat  higher  temperature.  It  is  insoluble  in  water  but  easily 
soluble  in  methyl  and  amyl  alcohols,  acetone,  ether,  chloroform, 
carbon  disulphide  and  fixed  and  volatile  oils.  Because  of  its 
acid  nature  it  dissolves  readily  in  solutions  of  the  alkalis  forming 


ROSIN  265 

salts  which  are  similar  to  those  of  the  higher  fatty  acids  or 
soaps. 

Rosin  contains  practically  no  ash.  Its  acid  number  varies 
from  155  to  175  and  averages  about  164;  this  corresponds  to 
83.4  to  93.8  per  cent  of  acid  of  the  formula  C2oH30O2.  The  unsa- 
ponifiable  matter  present  ranges  from  4  to  10  per  cent.  Accord- 
ing to  Schwalbe  and  Kiiderling,  rosin  contains  from  o.i  to  6.7  per 
cent  of  matter  insoluble  in  petroleum  spirit.  This  insoluble  mat- 
ter is  formed  very  rapidly  when  powdered  rosin  is  exposed  to 
sunlight  and  as  it  is  friable  and  devoid  of  sizing  power  its  amount 
should  be  as  low  as  possible.  Colophony  varies  more  or  less  in 
chemical  composition  but  its  chief  constituent  is  a  monobasic 
acid  of  the  formula  C2oH3oO2,  variously  spoken  of  as  abietic,  sylvic 
or  pimaric  acid. 

Because  of  the  growing  scarcity  of  rosin  and  its  increasing  price 
considerable  attention  is  being  paid  to  its  preparation  by  extrac- 
tion processes  from  the  "  lightwood"  and  stumps  of  longleaf  pine. 
There  are  on  the  market  a  number  of  rosins  prepared  in  such 
ways  and  from  a  superficial  examination  it  is  difficult  to  dis- 
tinguish them  from  those  made  in  the  regular  manner  from 
crude  turpentine.  The  acid  number  of  such  rosins  is  low,  sam- 
ples tested  by  the  author  giving  numbers  between  153  and  157, 
while  the  unsaponifiable  matter  may  run  as  high  as  11.2  per  cent. 
These  rosins,  when  crushed  or  cooked  for  size,  have  an  unmis- 
takable odor  of  pine  oil  and  this  odor  persists  even  into  the 
finished  paper  if  it  is  hard  sized.  They  have  been  found  to 
saponify  rather  more  slowly  than  the  regular  grades  and  the  size 
prepared  from  them  must  be  boiled  longer  in  consequence.  The 
alum  precipitate  from  such  sizes  has  a  distinct  greenish  color  in 
comparison  with  the  creamy  white  shade  of  that  from  ordinary 
size.  Considering  the  small  amount  of  rosin  generally  used  in 
paper  this  is  not  a  serious  fault.  Practical  trials  of  such  rosins 
have  demonstrated  that  while  they  may  give  excellent  results  at 
times  yet  they  are  not  entirely  reliable. 

The  method  of  making  rosin  size  varies  more  or  less  with  dif- 
ferent mills  but  the  principle  on  which  all  are  based  is  that  of 


266  SIZING 

combining  the  acid  rosin  with  an  alkali  to  render  it  soluble. 
Among  the  alkalis  suggested  are  sodium  aluminate  and  sodium 
silicate  which  are  sufficiently  alkaline  to  dissolve  the  rosin  when 
their  solutions  are  boiled  with  it.  Size  prepared  with  these 
alkalis  precipitates  alumina  or  silica  on  treatment  with  an  acid 
or  alum  and  these  two  substances  aid  in  filling  the  paper  and 
imparting  hardness  and  rattle.  The  alkali  commonly  used  how- 
ever is  soda  ash  which  is  obtainable  in  a  high  state  of  purity  and 
which  is  said  to  give  better  results  than  caustic  soda.  The  rela- 
tive value  of  these  two  probably  depends  on  local  conditions  to 
some  extent  but  it  has  been  the  author's  experience  that  for  equal 
weights  of  rosin  the  size  made  with  caustic  soda  was  much  more 
efficient  than  the  other.  One  very  general  mode  of  operation  is 
that  of  boiling  in  an  open  kettle  fitted  with  a  steam  coil  or  jacketed 
around  the  bottom.  The  rosin  may  be  added  first  and  when  it 
has  all  melted  the  soda  ash  dissolved  in  the  desired  amount  of 
water  may  be  run  in,  little  by  little,  or  the  soda  ash  may  first  be 
dissolved  in  the  kettle  and  then  the  crushed  rosin  added  to  the 
boiling  solution.  The  time  of  boiling  varies  in  different  mills 
from  three  to  seven  hours  but  even  with  very  long  boiling  it  is 
probably  not  possible  to  cause  all  of  the  soda  ash  to  combine  with 
the  rosin,  so  that  the  final  product  generally  contains  both  free 
rosin  and  uncombined  soda.  In  one  mill  where  400  Ibs.  of  soda 
ash  were  used  for  2,000  Ibs.  of  rosin  and  the  boiling  continued  for 
about  three  hours  the  size  made  analyzed  as  follows: 


Freshly  prepared 

Ready  to  use 

Combined  rosin 

Per  cent 

22  .O 

Per  cent 

30.  «; 

Free  rosin 

II  .  •? 

1C  .0 

Combined  soda,  Na2O        .        

3  -° 

4-5 

Free  soda,  Na2CO3     

3  -4 

1  .2 

Water  by  difference  

60.3 

47  .9 

It  was  formerly  the  general  custom  to  use  a  neutral  size,  or  one 
in  which  the  rosin  was  all  combined  with  soda,  but  more  recent 
practice  calls  for  one  containing  more  or  less  free  or  uncombined 


ROSIN  SIZE  267 

rosin.  The  amount  of  this  free  rosin  varies  with  the  manner 
in  which  the  size  is  to  be  used;  if  it  is  added  directly  to  the 
beater  without  first  dissolving,  the  limit  is  about  35  per  cent  of 
the  total  rosin  and  it  is  usual  to  run  considerably  lower.  If  an 
emulsifying  or  dissolving  apparatus  is  employed  the  percentage 
of  free  rosin  may  safely  go  as  high  as  45  per  cent.  The  theoretical 
percentage  of  sodium  carbonate  required  to  give  a  neutral  solu- 
tion with  pure  abietic  acid  is  17.5  but  if  this  amount  is  used  with 
commercial  rosin  the  size  will  still  contain  a  considerable  amount 
of  free  rosin;  hence  it  is  quite  general  to  use  an  even  larger 
amount  than  this.  With  high  free  rosin  sizes  for  use  in  erhulsi- 
fying  apparatus  the  amount  of  soda  may  go  as  low  as  seven  parts 
per  100  of  rosin. 

Neutral  size  is  generally  clear  and  dark  in  color  while  free  rosin 
sizes  may  be  clear  and  dark  or  opaque  and  light  colored.  If  a 
free  rosin  size  contains  about  50  per  cent  of  water  and  free  soda 
is  present,  the  size,  on  cooling,  will  separate  a  dark  reddish-brown 
liquid  containing  the  excess  of  soda  and  some  of  the  coloring 
matter  of  the  rosin.  This  separation  is  sometimes  caused  to  take 
place  by  adding  a  little  common  salt  to  the  size,  the  idea  being  to 
improve  the  color  of  the  paper.  It  is  doubtful  if  the  gain  in  color 
is  appreciable  since  this  dark  liquor  when  acidified  gives  a  pre- 
cipitate which  is  only  slightly  grayish  in  color.  The  proportion 
of  water  in  a  size,  besides  affecting  the  separation  of  the  black 
liquor,  is  also  of  importance  because  of  its  influence  on  the  con- 
sistency of  the  size,  which,  at  the  end  of  the  cook,  should  be 
sufficiently  fluid  to  strain  through  a  60  mesh  wire  screen.  It  is 
occasionally  found  that  a  size  is  too  thick  and  the  attempt  is 
made  to  thin  it  down  by  adding  water,  with  the  peculiar  result 
that  it  becomes  thicker  instead  of  thinner.  It  is  also  frequently 
noticed  that  a  size  containing  30  per  cent  of  water  boils  thinner 
than  one  with  50  per  cent  so  that  we  are  forced  to  the  conclusion 
that  a  thick  boil  usually  indicates  too  much,  rather  than  too  little, 
water. 

From  time  to  time  various  substances  have  been  proposed  as 
possible  additions  to  rosin  size.  Among  these  may  be  mentioned 


268  SIZING 

phenol,  phenanthrene  and  linseed  oil  to  cause  the  rosin  to  sapon- 
ify more  readily  and  to  give  a  better  emulsion,  and  starch,  glue, 
casein  and  horn  to  enhance  the  sizing  power  of  the  rosin.  Other 
suggested  materials  are  potato  meal,  albumen,  tannic  acid  and 

stearin>       ^^ 
r~~    —       j^ 
Size  is  .&§st  added  to  the  beater  after  the  stock  and  filler  are  in 

but  before  the  alum.  Still  better  sizing  results  are  said  to  be 
obtained  by  putting  the  size  in  the  beater  with  enough  water  to 
carry  it  under  the  roll  and  allowing  it  to  circulate  before  the 
stock  is  added.  This  however  causes  so  much  foaming  that  it 
is  impractical.  If  the  size  contains  less  than  35  per  cent  of  free 
rosin  it  may  be  added  directly  to  the  engine  or  it  may  first  be  dis- 
solved in  luke-warm  water.  Hot  water  should  never  be  used 
because  it  causes  the  free  rosin  to  collect  in  lumps  which  make 
spots  in  the  paper.  There  is  probably  not  much  to  choose  between 
adding  directly  to  the  beater  or  dissolving  so  far  as  efficiency 
of  sizing  goes  but  as  the  dissolved  size  may  be  strained  through 
cloth  it  is  preferable  from  the  standpoint  of  cleanliness.^ 

With  high  free  rosin  sizes  some  form  of  emulsifier  should  be 
used  in  order  that  the  emulsion  of  free  rosin  may  be  so  fine  that 
none  will  settle  out.  The  emulsifier  is  practically  a  steam  injector 
which  takes  the  hot  size  and  sprays  it  suddenly  into  a  large  body 
of  cold  water.  This  prevents  the  free  rosin  from  collecting  in 
flakes  and  gives  very  fine  particles  in  suspension.  Some  forms 
of  apparatus  are  so  arranged  that  the  operator  can  control  the 
output  and  obtain  at  will  either  a  milky  suspension  of  com- 
paratively coarse  particles  or  a  semi-transparent,  brownish  one 
in  which  the  particles  may  be  as  small  as  0.002  mm.  in  diameter. 
The  concentration  of  the  emulsion  is  said  to  have  a  large  influence 
on  the  results  and  the  upper  limit  for  satisfactory  work  is  vari- 
ously given  as  a  2  to  3  per  cent  solution  of  rosin.  The  claims 
made  for  emulsification  processes  are  more  uniform,  cheaper  and 
better  sizing  and  less  dirt.  In  this  country  many  mills  which 
formerly  added  their  size  directly  to  the  beater  are  installing 
emulsifying  apparatus  with  very  good  results. 
./  The  mere  presence  of  rosin  size  in  the  stock  does  not  mean 


FREE  ROSIN  IN  SIZE  269 

that  the  paper  will  be  sized;  to  accomplish  this  object  the  rosin 
must  be  precipitated  on  the  fibre  in  such  a  way  that  the  paper 
on  drying  will  be  water-resistant.  The  substances  which  will 
cause  precipitation  are  acids,  acid  salts  and  salts  of  the  alkaline 
earths  and  heavy  metals.  ^The  precipitants  which  have  been 
actually  proposed  from  time  to  time  include,  sulphuric  acid, 
sodium  acid  sulphate,  carbonic  acid,  zinc  sulphate,  magnesium 
sulphate,  calcium  chloride,  aluminum  sulphate,  etc.  Practical 
trials  have  proved. that  while  precipitation  with  acid  will  give 
fairly  good  sizing  the  results  are  by  no  means  so  permanent  as 
when  alum  is  used.  None  of  the  precipitants  having  an  alka- 
line base  as  copper,  lead,  or  zinc  will  give  good  results  nor  will 
the  salts  of  the  alkaline  earths,  as  magnesium  sulphate  or  calcium 
chloride  even  though  they  completely  precipitate  the  rosin. 
Tests  by  Pauli,  Frohberg  and  others  have  proved  that  magnesium 
sulphate,  whether  used  alone  or  as  a  partial  substitute  for  alum, 
has  no  value  as  a  sizing  agent  and  experiments  carried  out  under 
the  direction  of  the  author  have  shown  that  calcium  chloride  is 
equally  valueless.  In  practical  working  we  are  concerned  only 
with  alum  or  aluminum  sulphate  which  is  the  precipitant  univer- 
sally employed  in  rosin  sizing. 

Researches  by  Wlirster  in  1878  led  him  to  the  conclusion  that 
the -prime  sizing  agent  was  the  free  rosin  thrown  down  by  the 
alum  and  on  the  basis  of  these  experiments  much  stress  has  been 
laid  on  the  use  of  sizes  high  in  free  rosin.  This  question  has 
never  been  definitely  settled  and  there  is  still  much  difference  of 
opinion  as  to  whether  the  sizing  agent  is  free  rosin  or  aluminum 
resinate.  Our  experience  has  been  that,  other  things  being  equal, 
a  pound  of  rosin  as  neutral  size  has  as  much  sizing  power  as  a 
pound  in  the  form  of  size  containing  30  per  cent  of  its  rosin  in  the 
free  state.  This  does  not  necessarily  mean  that  the  sizing  agent 
is  not  free  rosin,  since  the  latter  may  be  formed  by  the  reaction 
with  alum,  but  it  does  indicate  that  too  much  importance  is 
placed  on  the  presence  of  free  rosin  in  the  size.  The  reaction 
between  rosin  size  and  alum  has  been  studied  by  Remington,1 

1  Remington,  Bowack  and  Davidson:  J.  Ind.  Eng.  Chem.,  1911,  3,  466. 


270  SIZING 

Schwalbe,1  Neugebauer,2  Heuser  3  and  many  others  with  quite 
conflicting  results.  Even  when  considering  the  case  of  neutral 
size  and  alum  alone  there  is  marked  lack  of  agreement  and 
when  the  reaction  takes  place  in  the  presence  of  cellulose  still 
further  complications  are  introduced  by  the  absorptive  power 
which  the  latter  has  for  alumina  and  which  Schwalbe  claims 
may  quantitatively  effect  the  decomposition  of  3  per  cent  of  its 
weight  of  aluminum  sulphate.  The  reaction  between  sodium 
resinate  and  alum  is  given  by  Heuser  as  follows: 

6  C2oH2902Na  +  Ala  (S04)3  =  3  Na2SO4  +  A12  (C20H2902)6. 

This  is  for  equivalent  quantities  and  indicates  the  formation 
of  aluminum  resinate.  If  an  excess  of  alum  is  used  free  rosin  is 
formed  as  follows: 

2  C20H29O2Na  +  H20  +  A12  (S04)3 

=  Na2S04  +  2  C2oH3o02  +  A120  (S04)2. 

In  the  presence  of  cellulose  these  reactions  are  doubtless 
somewhat  modified  and  it  seems  probable  that  free  rosin,  alu- 
minum resinate  and  alumina  all  play  a  part  in  producing  the 
final  result. 

The  relation  between  the  amount  of  alum  and  rosin  used  in 
the  engine  is  of  considerable  importance.  With  a  neutral  size 
it  was  found  that  0.202  Ib.  of  alum  (17  per  cent  A12O3)  was 
sufficient  to  precipitate  each  pound  of  rosin  while  with  a  31 
per  cent  free  rosin  size  the  figure  found  by  titration  was  0.201  Ib. 
In  actual  operations  these  proportions  are  never  even  approxi- 
mated for  if  they  are  the  paper  is  very  slack  sized  which  indi- 
cates the  necessity  of  inducing  secondary  reactions  between 
the  aluminum  resinate  and  the  alum.  It  has  been  found  by 
experience  that  the  ratio  of  alum  to  rosin  should  not  fall  much 
below  ij  :  i  if  good  sizing  is  to  be  expected,  and  this  has  been 
confirmed  by  laboratory  experiments  using  a  standard  fibre 

1  Schwalbe  and  Robsahm:  Wochbl.  Papierfabr.,  43,  1454. 

2  Neugebauer:  Z.  angew.  Chem.,  25,  2155. 

3  Heuser:  Wochbl.  Papierfabr.,  44,  1312,  1394,  1517,  1583,  1688. 


AMOUNT  OF  ROSIN  REQUIRED 


271 


furnish  and  an  amount  of  size  equivalent  to  i|  per  cent  of  rosin 
on  the  weight  of  fibre.    These  tests  gave  the  following  results: 


Percentage  of  rosin 

Percentage  of  alum 
(17  per  cent  AlzO3) 

Sizing 
Ink  test  in  seconds 

i-5 

I  .0 

14 

i-5 

2.0 

134 

1-5 

2-5 

195 

i-5 

3-° 

230 

i-S 

4.0 

228 

i-5 

6.0 

2  2O 

6.0 

4.0 

2IO 

6.0 

8.0 

566 

I 

The  extent  to  which  the  alum  may  be  reduced  is  also  lim- 
ited by  the  difficulty  which  is  caused  by  the  stock  sticking  to 
the  couch  and  presses  of  the  paper  machine.  Practical  trials 
on  a  book-paper  machine  showed  that  sticking  was  likely  to 
take  place  if  the  ratio  was  dropped  to  1.2  alum  to  i  rosin,  but 
that  it  ran  safely  if  the  ratio  was  1.5  :  i.  A  safe,  practical  test 
for  sufficiency  of  alum  is  to  have  the  stock  in  the  engine  react 
slightly  acid  to  litmus  paper  or  turn  alcoholic  Congo  red  solution 
slightly  brownish. 

Crhe  amount  of  rosin  used  in  sizing  paper  varies  greatly  with 
the  grade  being  made;  in  some  it  may  drop  as  low  as  0.25  per 
cent  of  the  stock  furnished  while  in  hard  sized  orders  it  may 
amount  to  2  per  cent  or  even  more.)  The  sizing  increases  with 
the  quantity  of  rosin  used  as  is  seen  from  the  following  figures, 
which  were  obtained  by  sizing  a  mixture  of  one-half  soda  poplar 
and  one-half  sulphite  spruce  beaten  together  in  a  standard 
manner. 


Per  cent  of  rosin  on 
fibre  furnish 

Per  cent  of  alum  on 
fibre  furnish 

Ink  test  in  seconds 

0.38 

4 

12 

0-75 

4 

45 

1-50 

4 

226 

3.00 

4 

380 

6.00 

8 

566 

272 


SIZING 


The  increase  in  sizing  is  not  proportional  to  the  increase  in 
rosin  throughout  the  series,  the  greatest  gain  being  obtained 
when  the  rosin  is  increased  from  0.75, to  1.50  per  cent. 

The  sizing  of  paper  containing  18  per  cent  of  ash,  as  well  as 
that  of  the  above  series  of  tests,  is  illustrated  in  Fig.  35  which 
shows  the  marked  difference  caused  by  the  filler.  This  indi- 
cates the  waste  of  materials  by  using  much  more  than  2\  per 
cent  of  rosin  in  paper  which  is  heavily  loaded. 


A 


Un 


illel  Paper 


Filled  Paper 


M  4 
a  * 


s/ 


7 


60     120    180    240    300    360    420 
Ink  Test  in  Seconds 

FIG.  35. 


480 


540 


600 


Trouble  in  sizing  is  frequently  encountered  in  hot  weather 
and  particularly  in  engines  where  the  stock  tends  to  become 
heated.  This  is  probably  due  to  the  rosin  particles  uniting  to 
form  larger  masses  which  do  not  cover  the  fibres  well.  In 
such  cases  the  size  should  be  added  to  the  stock  as  late  as  pos- 
sible. Water  containing  calcium  bicarbonate,  or  the  presence 
of  calcium  carbonate  or  calcium  hydroxide  in  the  stock,  is  par- 
ticularly bad  for  sizing,  while  calcium  sulphate  or  chloride  has 
practically  no  influence  on  the  result.  With  the  latter  salt, 
even  as  much  as  5  per  cent  on  the  weight  of  the  fibre,  has  been 
found  to  be  harmless  though  much  less  than  this  amount  will 


ROSIN  273 

completely  precipitate  the  average  amount  of  size  used.  This 
is  probably  to  be  explained  on  the  assumption  that  the  alum 
subsequently  added  reacts  with  the  calcium  resinate  forming 
free  rosin,  calcium  sulphate  and  alumina.  This  is  a  very  for- 
tunate circumstance  since  the  bleached  fibre  employed  often 
introduces  more  than  enough  calcium  chloride  from,  the  ex- 
hausted bleach  to  precipitate  all  the  size  used.  Other  disturb- 
ing factors  are  the  soluble  matters  washed  into  the  water  supply 
by  heavy  rains,  the  presence  of  much  filler,  or  of  acid  from 
incompletely  washed  sulphite  fibre,  etc.  The  influence  of  the 
filler^  is  well  illustrated  by  the  curve  on  page  291. 

/The  sizing  process  is  not  completed  till  the  web  of  paper  has 
passed  over  the  driers  and  the  manner  of  conducting  this  opera- 
tion has  a  great  influence  on  the  results.  The  best  conditions 
are  said  to  be  moderate  steam  pressure  on  the  first  drier,  increas- 
ing to  a  maximum  at  about  the  middle  of  the  bank  and  again 
decreasing  toward  the  calenders.  This  warms  the  paper  up 
gradually  but  permits  it  to  reach  a  high  temperature  before 
the  moisture  is  driven  off,  which  has  been  found  essential  to 
good  sizing^  If  the  first  driers  are  too  hot  the  sudden  escape 
of  steam  opens  up  the  pores  of  the  paper  and  the  sizing  is 
defective,  while  if  the  paper  becomes  too  dry  before  the  proper 
temperature  is  reached  the  sizing  is  also  poor.  Moist  heat 
seems  to  be  a  requisite  of  good  sizing  and  slack  sized  paper 
may  often  be  greatly  improved  by  exposing  it  to  steam  even 
at  as  low  a  temperature  as  100°  C. 

Experiments  by  the  author  on  the  drying  of  sized  pulp  taken 
from  the  first  press  of  a  paper  machine  gave  quite  different 
results  from  those  of  other  observers.  The  drier  was  a  sta- 
tionary cylinder  heated  by  steam  and  the  sheets  to  be  dried 
were  held  against  its  surface  by  a  tightly  stretched  piece  of  old 
press  felt.  Two  grades  of  paper  were  tested  at  various  tem- 
peratures with  the  following  results : 

1  Klemm:  Wochbl.  Papierfabr.,  39,  1908,  p.  1369. 


274 


SIZING 


Sizing:  seconds  for  ink  to  penetrate 

Temperature  of  drier 

Sample  I 

Sample  2 

Deg.  C. 

IOO 

43° 

260 

106 

480 

280 

112 

510 

270 

H9 

420 

260 

131 

440 

250 

142 

420 

240 

152 

420 

240 

All  these  samples  were  held  against  the  cylinder  until  steam- 
ing ceased  and  were  then  exposed  to  the  air  for  twenty-four 
hours  before  testing  for  sizing.  It  was  also  demonstrated  in 
these  experiments  that  if  the  paper  were  alternately  pressed 
against  the  cylinder  and  removed,  as  would  be  the  case  in 
passing  over  the  driers  of  a  paper  machine,  the  sizing  was  only 
one-third  to  one-half  as  strong  as  though  it  had  been  held 
against  the  drier  continuously. 

This  question  of  the  relation  between  the  manner  of  drying 
and  the  sizing  of  the  sheet  is  one  on  which  little  work  has  appar- 
ently been  done,  but  it  is  one  which  must  be  investigated  much 
more  carefully  before  it  will  be  possible  to  say  that  the  best 
conditions  for  sizing  are  maintained. 

Defects  of  Rosin  Sizing.  It  is  the  general  opinion  that  the 
presence  of  rosin  in  paper  causes  more  or  less  rapid  deteriora- 
tion according  to  the  amount  present.  Much  work  has  been 
done  in  the  attempt  to  prove  this  point  and  to  determine  the 
maximum  amount  which  it  is  safe  to  employ,  but  beyond  the 
general  conclusion  that  it  is  injurious  if  used  in  large  amount 
there  is  little  agreement  between  different  observers.  Under 
the  action  of  oxygen  rosin  forms  a  substance  having  the  nature 
of  peroxide  which  then  acts  on  cellulose  forming  oxycellulose 
and  injuring  the  paper.  This  action  is  said  to  be  more  vigorous 
with  the  original  rosin  in  ground  wood  than  with  that  which  has 
been  made  into  size  and  reprecipitated.  The  discoloration  of 
paper  is  also  ascribed  to  the  rosin  but  all  attempts  to  devise  a 


TESTING  OF  ROSIN  AND   ROSIN  SIZES  275 

positive  test  which  will  show  whether  rosin  sized  papers  will 
become  yellow  have  thus  far  failed.  Zschoke  L  concludes  that 
wood-free  paper  with  not  over  i  per  cent  of  rosin  will  not  be- 
come yellow,  while  Klason2  thinks  that  papers  properly  sized 
with  rosin  will  not  be  injured  within  sixty  years. 

If  rosin  sized  paper  is  exposed  to  sunlight  the  sizing  is  de- 
stroyed and  the  paper  becomes  absorbent.  This  is  also  true 
of  animal  sized  papers  though  the  change  is  not  so  rapid.  With 
rosin  sizing  this  is  undoubtedly  due  to  the  formation  of  the 
friable  substance,  insoluble  in  petroleum  ether,  which  has  been 
previously  mentioned.  The  use  of  a  small  amount  of  tannin 
with  the  size  is  said  to  cause  this  change  to  take  place  much 
more  slowly. 

Defective  sizing  may  also  be  caused  by  calendering  as  this 
has  been  found  to  reduce  the  resistance  to  ink  from  6  to  40 
per  cent.  Other  factors  which  may  cause  defective  sizing  are 
too  much  filler,  improper  proportion  of  alum  and  poorly  cooked 
size.  These  are  all  well-defined  troubles  and  can  be  readily 
corrected  but  there  are  also  defects  which  come  from  causes  so 
obscure  as  to  practically  defy  detection  and  for  which  little  can 
be  done. 

Testing  of  Rosin  and  Rosin  Sizes.  In  testing  rosin  for  use  in 
size  making  one  of  the  most  important  determinations  is  that 
of  the  acid  number,  which  is  the  number  of  milligrams  of  caustic 
potash  required  to  neutralize  i  gram  of  rosin.  This  is  best  de- 
termined by  dissolving  a  weighed  sample  of  the  rosin,  in  neutral 
alcohol  and  titrating  directly  with  alcoholic  KOH  solution,  us- 
ing phenolphthalein  as  indicator.  With  average  American  rosin 
about  164  milligrams  of  KOH  will  be  required  for  every  gram 
of  rosin.  This  test  indicates  roughly  the  amount  of  alkali 
which  the  rosin  will  use  up  in  the  ordinary  size-making  process 
and  it  may  be  used  as  the  basis  for  calculating  the  reduction 
in  the  amount  of  alkali  which  should  give  a  size  with  a  definite 
percentage  of  free  rosin. 

1  Wochbl.  Papierfabr.,  44,  2976  and  3165. 

2  Paper  Trade  J.,  1913,  p.  46. 


276  SIZING 

The  unsaponifiable  matter  may  be  determined  by  heating  a 
sample  on  the  steam  bath  for  several  hours  with  an  excess  of 
caustic  potash  solution,  cooling,  extracting  with  ether,  as  in  the 
case  of  size,  evaporating  off  the  ether,  drying  and  weighing. 
This  unsaponifiable  matter  is  soft  and  sticky  in  character  and 
if  present  in  large  amount  is  likely  to  cause  trouble  by  sticking 
at  various  points  on  the  paper  machine. 

The  amount  of  material  insoluble  in  petroleum  ether  should 
be  determined  by  dissolving  a  weighed  sample  of  the  rosin  in 
petroleum  ether,  separating  the  solution  from  the  insoluble 
residue,  washing  the  latter  with  several  portions  of  ether,  dry- 
ing and  weighing.  The  insoluble  matter  has  practically  no 
sizing  properties  and  it  should  be  present  in  small  amount  only. 

In  the  case  of  rosin  size  containing  no  admixture  of  foreign 
material,  the  substances  to  be  determined  are  moisture,  free 
and  combined  rosin  and  free  and  total  alkali. 

Moisture  may  be  conveniently  determined  by  weighing  out 
2  to  3  grams  of  the(  size  in  a  covered  weighing  bottle,  dissolving 
in  hot  water,  transferring  to  a  weighed  platinum  dish,  evapo- 
rating to  dryness,  drying  and  weighing.  Total  alkali  may  then 
be  estimated  in  this  dry  sample  by  burning  off  the  organic 

N 
matter  and  titrating  the  residual  mineral  matter  with  —  acid 

using  methyl  orange  as  an  indicator.  For  free  alkali  weigh  out 
10  grams  of  size  and  dissolve  in  200  c.c.  of  acid  free  absolute 
alcohol.  Allow  to  stand  at  least  eight  to  ten  hours,  or  longer, 
if  possible,  and  filter,  washing  the  filter  with  absolute  alcohol. 
When  well  washed  pour  boiling  water  through  the  filter  and 

N 

titrate  the  aqueous  solution  with   -  -  acid  using  methyl  orange 

10 

as  an  indicator. 

Free  rosin  should  be  determined  in  a  5  to  10  gram  sample. 
Dissolve  in  a  small  amount  of  hot  water  and  wash  into  a  sepa- 
ratory  funnel  keeping  the  volume  of  water  as  small  as  possible. 
Cool,  add  about  25  c.c.  acid  free  ether,  shake  and  allow  to  stand 
till  the  ether  layer  separates  clear.  If  this  does  not  take  place 


ALUM  277 

readily  it  may  be  hastened  by  adding  a  few  drops  of  a  strong 
solution  of  sodium  chloride.  When  separation  has  taken  place 
draw  off  the  aqueous  solution  into  a  flask  and  wash  the  ether 
extract  twice  with  small  portions  of  water,  adding  these  wash- 
ings to  the  solution  in  the  flask.  Transfer  the  ether  extract  to 
a  small  weighed  dish  or  flask  and  replace  the  aqueous  solution 
in  the  separatory  funnel.  Repeat  the  extraction  with  ether  and 
add  the  second  extract  to  the  first  in  the  weighed  dish.  Care- 
fully evaporate  the  ether,  dry  the  residue  at  105°  C.  for  about 
two  hours,  cool  and  weigh  as  free  or  uncombined  rosin. 

Combined  rosin  may  be  determined  in  the  soap  solution 
remaining  after  the  extraction  of  the  free  rosin.  Add  sufficient 
acid  to  completely  free  the  rosin  and  then  extract  with  ether  as 
in  the  case  of  free  rosin.  For  this  determination  it  is  probably 
well  to  extract  three  times  with  25  c.c.  of  ether  instead  of  twice 
as  for  free  rosin. 

A  useful  qualitative  test  for  size  containing  free  rosin  is  car- 
ried out  by  stirring  hike-warm  water  into  the  size,  a  little  at  a 
time,  until  a  thin  milk  is  produced  and  then  pouring  this  into 
a  large  jar  of  cold  water.  If  during  the  dissolving  the  rosin 
separates  in  lumps,  or  if  on  standing  for  an  hour  after  dilution 
flakes  settle  to  the  bottom,  the  size  is  unsafe  to  use  unless  some 
sort  of  an  emulsifier  is  employed. 

In  addition  to  the  tests  already  described,  commercial  sizes 
must  be  examined  for  such  substances  as  starch,  glue,  casein, 
gum,  dextrine,  etc.  All  these  are  insoluble  in  alcohol  and  may 
therefore  be  looked  for  in  the  residue  left  on  dissolving  the  size 
in  strong  alcohol.  The  character  of  this  residue  will  generally 
give  some  indication  as  to  the  nature  of  the  substances  present 
and  special  tests  may  then  be  applied  for  those  which  are 
suspected.1 

Alum.  As  already  mentioned  the  rosin  sizing  process  necessi- 
tates the  use  of  some  precipitant  and  the  agent  universally  em- 
ployed is  aluminum  sulphate,  or  alum,  as  it  is  generally  called  in 
the  paper  industry.  Alum  is  manufactured  largely  from  clay  and 

1  J.  Marcusson:  Chem.  Rev.  Fett.  Ind.,  1914,  21,  1-3. 


278  SIZING 

bauxite  by  treatment  with  sulphuric  acid.  If  calcined  clay  is 
added  to  sulphuric  acid  of  1.48  sp.  gr.  at  85°  C.  a  vigorous 
reaction  immediately  takes  place  and  the  resulting  mass  after 
agitation  and  standing  gradually  solidifies.  About  60  per  cent 
of  the  alumina  present  in  the  clay  is  converted  to  sulphate. 
The  product  known  as  "alum  cake"  contains  all  the  impurities 
of  the  clay  and  according  to  Bailey  its  average  composition  is 

Per  cent 
A12O3  (soluble) 12. 3-13. o 

FC2Os O.I-   O.  2 

SO3  (combined) 29. 5-3 1 . 8 

SO3  (free) 0.4-1.0 

Insoluble 20. 0-26.  5 

Alum  cake  is  sometimes  purified  by  lixiviation,  separation  of  the 
clear  liquid  and  evaporation  to  about  1.56  sp.  gr.  at  115°  C., 
when  on  cooling  it  sets  in  solid  blocks. 

The  procedure  with  bauxite  is  very  similar  except  that  it  is 
boiled  with  the  acid  for  several  hours,  diluted  to  1.35  sp.  gr.  at 
the  boiling  point,  separated  from  insoluble  matter,  and  then 
concentrated.  The  alum  from  bauxite  may  contain  up  to  0.7 
per  cent,  or  even  more,  of  Fe20s  and  no  entirely  satisfactory 
method  of  freeing  it  from  this  impurity  has  yet  been  devised. 

For  the  preparation  of  pure  aluminum  sulphate,  powdered 
bauxite  is  mixed  with  so  much  soda  ash  that  for  each  molecule 
of  AUOs  (including  Fe203)  there  are  present  i  to  1.2  molecules 
of  Na2O.  The  mixture  is  then  heated  in  a  reverberatory  furnace 
with  frequent  stirring  for  five  hours.  On  lixiviating  the  result- 
ant mass  a  solution  of  sodium  aluminate  is  obtained  while  the 
iron  remains  as  Fe20s  in  the  insoluble  residue.  Passage  of 
carbon  dioxide  through  the  solution,  or  its  treatment  with  alu- 
mina (Bayer's  process),  causes  the  separation  of  alumina  which 
on  solution  in  sulphuric  acid  gives  an  alum  containing  only  o.oi 
to  0.02  per  cent  of  Fe203.  A  product  containing  less  than  o.oi 
per  cent  Fe2O3  is  generally  called  free  from  iron. 

In  making  alum  zinc  is  sometimes  added  to  reduce  the  iron 
to  the  ferrous  state,  in  which  condition  it  imparts  only  a  slight 


ALUM 


279 


greenish  color  to  the  product.  The  presence  of  free  acid  also 
tends  to  mask  the  presence  of  iron.  If  the  alum  is  basic,  0.05 
per  cent  of  Fe203  gives  a  yellowish  color  and  if  0.15  per  cent  is 
present,  the  basic  ferric  salts  color  the  alum  as  dark  as  bees- 
wax, while  if  free  acid  is  present  this  amount  of  iron  scarcely 
colors  the  alum  at  all. 

Characteristic  analyses  of  alum  are  as  follows: l 


i 

2 

3 

4 

s 

6 

7 

Insoluble  in  water  

O.4Q 

o  .06 

0.67 

0.18 

o  .4 

o.  16 

Alumina   AlaOs 

14    7O 

c 
ID    2O 

18  81 

22    37 

l6    32 

17   4 

*2I    87 

Iron,  Fe2Os  

O.I2 

O.O6 

0.80 

0.59 

0.51 

trace 

o  .40 

Zinc  oxide   ZnO 

3    80 

Soda   Na2O 

I     24 

o  76 

o  67 

o  84 

Sulphuric  acid,  SO3: 
Combined  

34   60 

36.62 

AC   qy 

4^.28 

36    QO 

3Q    2 

4Q   27 

Free              

o  40 

I   03 

Water  

40  .  qc 

4^  -  2Q 

32.  <8 

27  .  34 

4^  .42 

43    O 

27  .46 

In  interpreting  the  analysis  of  an  alum  it  is  to  be  noted  that 
a  large  amount  of  insoluble  matter  indicates  that  the  original 
raw  material  was  not  thoroughly  broken  down  by  the  acid  or 
that  the  purification  was  improperly  conducted.  Zinc  precipi- 
tates its  equivalent  of  size  but  it  is  seldom  present  in  sufficient 
amount  to  have  much  influence  on  the  value  of  the  alum,  while 
soda  is  usually  due  to  the  use  of  carbonate  in  the  manufacture 
of  porous  alum  but  may  also  be  derived  from  the  soda  used  in 
the  reverberatory  charge. 

The  presence  of  much  iron  in  an  alum  has  a  deleterious  effect 
on  the  color  of  the  paper  and  probably  also  on  its  permanence, 
and  its  amount  is  therefore  a  matter  of  some  importance. 
Authorities  differ  as  to  the  permissible  amount  of  iron,  but  the 
general  opinion  seems  to  be  that  for  news  papers  the  Fe2Os 
should  not  exceed  i  per  cent  and  that  not  over  0.05  per  cent 
should  be  in  the  ferric  state,  for  good  writing  or  book  papers 

1  Analysis  of  sample  i  from  Cross  and  Bevan,  "Text  Book  of  Paper  Making," 
samples  2,  3  and  4  from  Griffin  and  Little,  "Chemistry  of  Paper  Making,"  5,  6 
and  7  from  analyses  by  the  author. 


280  SIZING 

0.2  to  0.3  per  cent  should  be  the  upper  limit  and  it  should  pref- 
erably be  in  the  ferrous  condition.  For  only  the  highest  class 
of  papers  is  it  necessary  to  have  less  than  0.2  per  cent  of  Fe2O3 
and  then  the  limit  should  be  set  at  o.oi  per  cent.  While  the 
appearance  of  an  alum  is  improved  by  the  reduction  of  the  iron 
to  the  ferrous  state  it  is  probable  that  altogether  too  much 
stress  is  laid  on  this  point  as  the  processes  of  paper  making 
permit  its  rapid  oxidation  so  that  the  final  result  may  be  the 
same  no  matter  what  the  condition  of  the  iron  originally. 
'  The  amount  of  free  acid  in  alum  is  of  importance  because  of 
its  possible  effect  on  the  colors  used,  because  it  decomposes  the 
size  without  throwing  down  alumina  and  because  it  increases 
the  injurious  effect  of  the  alum  on  the  beater  bars  and  wires. 
If  present  in  excessive  amount  it  may  even  tend  to  weaken  the 
paper  as  it  passes  over  the  driers.  For  use  with  gelatine  in 
surface  sizing  alum  containing  free  acid  may  cause  brittleness 
of  the  paper  and  act  injuriously  on  the  metal  plates  used  in 
printing.  A  small  amount  of  free  acid  is  probably  harmless  in 
most  instances  but  it  should  be  limited  to  0.5  per  cent. 

The  value  of  an  alum  is  generally  considered  to  be  in  propor- 
tion to  the  amount  of  alumina  which  it  contains,  though  this  is 
no  indication  of  its  size  precipitating  power  since  impurities 
such  as  zinc  salts  and  free  acid  also  cause  precipitation  of  the 
roshij  A  neutral  or  slightly  basic  alum  is  also  preferred  to 
one  containing  free  acid  in  spite  of  the  fact  that  the  basic  alu- 
mina possesses  practically  no  size  precipitating  power.  A  basic 
alum  is  characterized  by  the  separation  of  alumina  on  dissolving 
to  a  dilute  solution. 

The  amount  of  alum  used  depends  on  a  number  of  factors 
besides  the  amount  of  size  employed.  Hard  water  necessitates 
additional  alum,  as  does  also  an  increase  in  the  temperature  of 
the  stock  in  the  beater.  The  quantity  to  use  is  generally  de- 
termined by  experience  rather  than  by  scientific  observation 
and  it  is  always  largely  in  excess  of  that  necessary  to  precipi- 
tate the  size.  This  excess  is  also  essential  in  order  to  prevent 
the  stock  from  sticking  to  the  press-rolls,  particularly  in  hot 


ALUM  281 

weather.  A  portion  of  the  alum  not  required  to  precipitate  the 
size  is  undoubtedly  decomposed  by  the  cellulose,  resulting  in  a 
fixation  of  alumina  on  the  fibres  but  that  a  considerable  part  is 
lost  is  proved  by  the  presence  of  aluminum  sulphate  in  the  back 
water.  For  an  engine  holding  1000  Ibs.  of  stock,  the  alum 
ordinarily  employed  in  sizing  would  range  from  12  to  30  Ibs.  or 
even  higher  for  very  hard  sized  papers. 

The  method  of  adding  the  alum  has  some  influence  on  the 
results  obtained,  it  being  found  best  to  allow  the  size  to  become 
thoroughly  mixed  with  the  stock  before  furnishing  the  alum. 
Some  mills,  however,  reverse  these  operations  and  add  the 
alum  first.  It  has  been  our  experience  that  this  gives  somewhat 
inferior  results  though  the  difference  is  not  very  great.  In  some 
establishments  it  is  also  customary  to  add  part  of  the  alum 
before  the  size  and  the  rest  afterwards  on  the  theory  that  any 
combination  of  size  with  lime  salts  will  be  prevented  by  the 
stronger  reactivity  of  the  alum.  Experience  has  shown  that 
even  if  sufficient  calcium  chloride  is  present  to  combine  with 
all  the  size,  subsequent  addition  of  alum  breaks  down  this  com- 
bination and  gives  fully  as  good  sizing  as  in  the  entire  absence 
of  calcium  chloride.  The  method  of  divided  alum  is  said  also 
to  reduce  frothing  and  on  this  basis  may  be  justified. 

If  possible  alum  should  be  used  in  the  form  of  a  solution  as 
this  promotes  rapid  mixing  with  the  stock.  It  is  stated  by 
Hoffman  that  the  solution  should  never  be  used  hot  or  stronger 
than  6°  Be.  The  alum  solutions  may  be  readily  prepared  from 
either  ground  or  ingot  alum  and  should  be  stored  in  either  wood 
or  lead-lined  tanks  and  distributed  through  lead  or  lead-lined 
pipes.  In  spite  of  the  obvious  advantages  of  distributing  from 
a  central  dissolving  station,  many  mills  still  add  the  ground  alum 
directly  to  the  beaters.  The  time  of  adding  the  alum  is  a  com- 
promise between  two  factors;  it  should  be  added  as  early  as 
possible  to  give  plenty  of  time  to  complete  its  reaction  with  the 
size  and  it  should  be  put  in  as  late  as  possible  to  prevent  action 
on  the  beater  bars  and  bed  plates.  If  bronze  bars  are  used  this 
second  factor  is  eliminated  and  the  alum  can  be  added  sooner. 


282  SIZING 

Testing  Alum.  The  analysis  of  alum  may  be  conveniently 
carried  out  according  to  the  following  scheme. 

Insoluble  matter  is  determined  by  dissolving  10  grams  of  the 
alum  in  a  small  quantity  of  water  and  filtering  at  once  through 
a  weighed  filter  into  a  liter  flask.  After  washing  the  filter 
thoroughly  with  hot  water  it  is  dried  at  105°  C.  and  weighed. 
The  difference  between  this  weight  and  the  original  weight  in 
grams  multiplied  by  10  gives  the  percentage  of  insoluble  matter. 

The  filtrate  and  washings  from  the  determination  of  insoluble 
matter  should  be  made  up  to  1000  c.c.  and  thoroughly  mixed; 
each  100  c.c.  of  this  solution  will  then  represent  exactly  i  gram  of 
alum. 

For  the  determination  of  total  sulphuric  anhydride,  SOs,  100 
c.c.  of  the  alum  solution  are  diluted  to  about  300  c.c.  and  a  few 
cubic  centimeters  of  dilute  hydrochloric  acid  added.  The  solu- 
tion is  now  heated  to  boiling  and  hot  barium  chloride  solution 
added  in  slight  excess.  After  digesting  on  the  steam  bath  for 
several  hours  the  precipitated  BaSO4  is  filtered  off,  washed  free 
from  chlorides,  dried  and  ignited  in  a  platinum  crucible.  After 
the  carbon  has  all  burned  off  the  crucible  is  cooled  and  its  con- 
tents moistened  first  with  a  few  drops  of  concentrated  nitric 
acid  and  then  with  a  drop  or  two  of  strong  sulphuric  acid.  The 
acids  are  then  very  cautiously  evaporated  and  the  crucible 
ignited  for  a  few  minutes  at  a  dull  red  heat,  cooled  and  weighed. 
The  percentage  of  sulphuric  anhydride  is  obtained  by  multiply- 
ing the  weight  of  precipitate  in  grams  by  34.30. 

The  total  iron  is  best  determined  by  a  colorimetric  method 
adapted  from  that  of  Stokes  and  Cain  l  and  using  a  colorimeter 
in  which  the  solutions  to  be  compared  are  contained  in  two 
test  tubes  of  the  same  diameter.  For  comparison  with  the 
alum  a  solution  containing  o.io  gram  ferrous  iron  per  liter  is 
made  by  dissolving  0.7026  gram  ferrous  ammonium  sulphate 
in  a  liter  of  water.  Into  one  of  the  test  tubes  10  c.c.  of  this 
solution  is  put,  together  with  10  c.c.  water,  5  c.c.  sulphocyanic 
acid  solution  (saturated  with  mercuric  sulphocyanate) ,  o.oi 

1  Stokes  and  Cain:  J.  Am.  Chem.  Soc.,  1907,  29,  409. 


TESTING  ALUM  283 

gram  ammonium  persulphate  and  10  c.c.  amyl  alcohol.  Into 
the  other  tube  0.5  c.c.  of  alum  solution  is  run  from  a  10  c.c. 
burette  and  then  19.5  c.c.  water,  5  c.c.  sulphocyanic  acid  solu- 
tion, o.oi  gram  ammonium  persulphate  and  10  c.c.  of  amyl 
alcohol  are  added.  Both  tubes  are  then  thoroughly  shaken 
and  comparison  of  the  colors  is  made  in  the  colorimeter  as  soon 
as  the  amyl  alcohol  layer  clears.  If  the  color  of  the  alum  solu- 
tion is  weak  it  is  adjusted  to  the  standard  by  adding  alum 
solution,  o.i  c.c.  at  a  time,  and  shaking  well.  If  the  alum 
tube  shows  too  strong  a  color  the  alum  solution  may  be  added 
to  the  standard  iron  tube  till  the  two  match.  By  dividing 
0.00002  by  the  grams  of  alum  in  the  alum  tube  (or  by  this 
number  minus  the  grams  added  to  the  iron  standard  tube)  and 
multiplying  this  quotient  by  100,  the  percentage  of  iron  in  the 
alum  is  obtained.  This  percentage  multiplied  by  1.43  gives 
the  total  iron  calculated  as  ferric  oxide,  Fe2O3. 

For  the  determination  of  alumina  in  the  absence  of  zinc,  100 
c.c.  of  the  alum  solution  are  diluted  to  about  300  c.c.  and  treated 
with  a  few  cubic  centimeters  of  dilute  hydrochloric  acid  and  a 
few  drops  of  concentrated  nitric  acid  to  oxidize  the  iron.  The 
solution  is  brought  to  the  boil,  5  c.c.  ammonium  chloride  added 
and  then  ammonium  hydroxide  with  constant  stirring  until  the 
solution  smells  slightly  of  ammonia.  After  heating  on  the 
steam  bath  5  minutes  —  when  a  faint  odor  of  ammonia  should 
still  be  noticeable  on  stirring  —  the  solution  is  filtered,  the  pre- 
cipitate washed  free  from  chlorides,  dried,  and  ignited  over  a 
blast  lamp  to  constant  weight.  This  weight  multiplied  by  100 
gives  the  percentage  of  alumina  and  ferric  oxide  and  by  sub- 
tracting the  percentage  of  the  latter,  already  found  by  the 
colorimetric  method,  the  per  cent  of  alumina  may  be  found. 

If  zinc  is  absent  the  filtrate  from  the  alumina  precipitate  may 
be  used  for  the  determination  of  alkalis.  The  solution  is  evapo- 
rated to  dryness  in  a  weighed  platinum  dish,  ignited  to  drive  off 
ammonium  salts,  cooled,  treated  with  a  little  concentrated  hydro- 
chloric acid  and  taken  up  with  a  little  water.  A  few  drops  of 
concentrated  sulphuric  acid  are  added,  and  the  solution  evapo- 


284  SIZING 

rated  as  far  as  possible  on  the  steam  bath.  The  dish  and  con- 
tents are  then  carefully  ignited  to  drive  off  sulphuric  acid,  heated 
a  few  moments  to  dull  redness,  cooled  and  weighed.  The 
weight  of  sodium  sulphate  thus  obtained  multiplied  by  43.64 
gives  the  percentage  of  sodium  oxide  in  the  alum. 

The  presence  of  zinc  in  an  alum  renders  the  above  procedure 
for  alumina  inaccurate  and  a  qualitative  test  for  zinc  should 
therefore  be  made  before  proceeding  with  the  alumina  deter- 
mination. To  a  moderately  strong  solution  of  the  alum  add 
an  excess  of  ammonia,  heat  to  boiling  and  filter.  To  the  clear 
nitrate  add  a  few  drops  of  ammonium  sulphide  and  heat  to  boil- 
ing. If  zinc  is  present  a  flocculent  white  precipitate  will  form 
which  on  boiling  a  few  minutes  will  settle  rapidly. 

In  the  presence  of  zinc  the  alumina  and  iron  should  be  deter- 
mined by  the  basic  acetate  method.  Dilute  100  c.c.  of  the  alum 
solution  to  500  c.c.,  add  2  grams  of  sodium  acetate  and  a  few 
drops  of  acetic  acid.  Bring  to  a  boil  and  keep  in  active  ebulli- 
tion for  ten  to  fifteen  minutes.  Allow  to  settle,  decant  the  clear 
liquid  through  a  filter  as  rapidly  as  possible  and  boil  up  the 
precipitate  with  water.  Repeat  the  settling,  decantation  and 
boiling  twice  more  and  finally  wash  the  precipitate  on  the  filter 
with  hot  water  containing  a  little  ammonium  acetate.  The 
filtrate  and  washings  are  evaporated  to  200  c.c.  and  if  any  pre- 
cipitate separates  it  should  be  filtered  off,  washed  and  united 
with  the  rest  of  the  precipitate  which  is  then  to  be  dried,  ignited 
and  weighed  as  above  described  for  alumina.  This  method 
also  gives  the  alumina  and  ferric  oxide  together  and  from  the 
total  weight  that  already  found  for  ferric  oxide  should  be 
deducted  in  order  to  give  the  alumina. 

In  the  filtrate  from  the  basic  acetate  precipitate  the  zinc  may 
be  determined  by  neutralizing  as  nearly  as  possible  with  ammonia, 
heating  to  boiling  and  adding  ammonium  sulphide  drop  by  drop 
so  long  as  a  precipitate  continues  to  form.  The  boiling  is  con- 
tinued fifteen  or  twenty  minutes,  the  zinc  sulphide  allowed  to 
settle  and  the  clear  liquor  tested  with  ammonium  sulphide  to 
make  sure  that  precipitation  is  complete.  If  such  is  the  case 


TESTING  ALUM  285 

filter  off  the  zinc  sulphide,  wash  with  hot  water  and  dry  the  filter 
in  the  oven.  Remove  the  precipitate  from  the  filter,  bum  the 
latter  over  a  porcelain  crucible,  add  the  zinc  sulphide  and  ignite 
with  free  access  of  air,  gently  at  first  but  finally  as  strongly  as 
possible.  The  occasional  addition  of  a  small  piece  of  ammonium 
carbonate  aids  the  operation  and  the  ignition  should  be  continued 
until  on  cooling  and  weighing  a  constant  weight  is  attained.  This 
weight  multiplied  by  100  gives  the  percentage  of  zinc  oxide  in 
the  alum. 

The  presence  of  free  acid  in  alum  is  indicated  by  a  blue  color 
with  Congo  red  solution;  if  free  acid  is  absent  a  dirty  brown 
color  only  results.  Craig  1  has  proposed  a  method  for  the  direct 
determination  of  free  acid  in  alum.  The  solutions  required  are: 
(i)  Potassium  fluoride  prepared  by  dissolving  the  pure  salt  in 
distilled  water  to  a  specific  gravity  of  1.45,  neutralizing  if  neces- 
sary with  caustic  potash  or  sulphuric  acid  until  i  c.c.  in  10  c.c.  of 
distilled  water  shows  a  faint  pink  with  phenolphthalein,  filtering 
and  diluting  the  clear  solution  to  a  specific  gravity  of  1.35.  This 
solution  should  be  preserved  in  glass  coated  with  wax.  (2)  Sul- 
phuric acid  standardized  against  sodium  carbonate  using  methyl 
orange  as  an  indicator.  (3)  Caustic  potash,  free  from  alumina 
and  similar  bases,  standardized  against  the  acid,  with  phenol- 
phthalein,  in  about  40  c.c.  of  water  to  which  10  c.c.  of  the  potas- 
sium fluoride  solution  have  been  added.  In  making  the  test 
a  weighed  portion  of  the  alum  is  dissolved  to  give  a  solution  of 
i  to  3  grams  of  alumina  in  200  c.c. ;  this  is  filtered  and  20  c.c.  are 
gradually  added,  with  stirring,  to  10  c.c.  of  the  potassium  fluoride 
solution,  to  which  50  to  60  c.c.  of  distilled  water  and  0.5  c.c.  of 
0.2  per  cent  solution  of  phenolphthalein  have  been  added.  When 
free  acid  is  present  the  mixture  is  practically  colorless  and  stand- 
ard alkali  is  slowly  added  until  a  faint  permanent  pink  color  is 
obtained;  the  amount  of  alkali  required  is  calculated  to  free 
acid. 

Moisture  in  alum  cannot  be  determined  by  direct  drying  or 

1  J.  Soc.  Chem.  Ind.,  1911,  30,  184. 


286  SIZING 

ignition;  it  is  generally  estimated  by  deducting  the  sum  of  the 
determined  substances  from  100  and  calling  this  difference  mois- 
ture. Griffin  and  Little1  recommend  the  following  method: 
Ignite  a  weighed  sample  of  alum  in  a  platinum  crucible  until  copi- 
ous fumes  of  SO3  appear,  cool,  weigh  and  note  the  loss.  Treat 
the  ignited  sample  with  hot  hydrochloric  acid  until  all  lumps  are 
broken  down,  filter,  and  wash  the  residue  with  hot  water.  The 
filtrate  and  washings  are  precipitated  with  barium  chloride  and 
the  sulphuric  acid  determined  as  usual.  The  percentage  of  SOs 
here  found,  deducted  from  the  total  (determined  in  a  separate 
sample),  gives  the  percentage  driven  off  by  ignition  and  this 
taken  from  the  total  loss  on  ignition,  in  per  cents,  leaves  the 
percentage  of  moisture  in  the  sample. 

The  size  precipitating  power  of  an  alum  may  be  ascertained  if 
desired  by  titrating  a  standard  size  solution  by  one  of  the  alum 
in  question.  This  test  gives  the  total  precipitating  power  of 
the  alum  and  makes  no  distinction  between  sulphates  of  alumina, 
iron,  or  other  bases  or  of  free  acid.  It  consequently  shows  little 
as  to  the  value  of  an  alum  and  its  usefulness  is  still  further  reduced 
by  the  fact,  already  mentioned,  that  a  considerable  excess  of 
alum  over  the  theoretical  must  always  be  used. 
\  Casein  Sizing.  Casein,  as  an  engine  size,  imparts  firmness, 
elasticity  and  strength  to  the  paper  and  enables  it  to  take  a  good 
finish.  It  aids  in  keeping  down  the  fuzz  on  the  surface  of  the 
paper  and  for  this  reason  may  form  a  partial  substitute  for  beat- 
ing. It  does  not  size  the  paper  in  the  same  sense  that  rosin  does 
as  the  precipitated  casein  is  not  water  repellent. 

Casein  being  an  insoluble  body  must  first  Be  brought  into 
solution  by  treating  with  an  alkali,  after  which  the  solution  may 
be  incorporated  with  the  rosin  size  or  it  may  be  added  directly  to 
the  beater.  In  either  case  the  addition  of  alum  to  the  stock 
causes  the  precipitation  of  a  bulky,  gelatinous  mass  which 
adheres  to  the  fibres  and  upon  drying  with  them  aids  in  filling 
the  pores.  Owing  to  the  nature  of  the  precipitated  casein  prac- 
tically all  of  it  is  retained  by  the  paper  and  when  as  little  as  2  per 

1  Chemistry  of  Paper  Making,  p.  382. 


VISCOSE  287 

cent  is  added  to  the  stock  its  presence  is  readily  detected  in  the 
finished  sheet. 

Unless  used  with  considerable  care  casein  is  apt  to  impart  an 
unpleasant  odor  to  the  paper.  If  used  in  too  large  proportions  it 
cements  the  fibres  together  so  firmly  that  the  folding  and  tearing 
strength  of  the  paper  is  considerably  reduced  though  at  the  same 
time  the  bursting  and  tensile  strength  is  increased.  Probably 
from  2  to  3  per  cent  is  the  maximum  which  can  be  used  without 
making  the  paper  brittle.  Because  of  these  drawbacks,  and  also 
because  of  the  comparatively  high  cost  of  the  material  ^casein 
sizing  is  not  generally  employed  and  may  be  said  to  be  used  only 
for  special  purposes^! 

I  Glue.  Glue  has  been  exploited  as  an  engine  size  in  much  the 
same  way  as  casein  and  for  the  same  reasons.  Unlike  casein,  how- 
ever, it  requires  only  hot  water  for  its  solution  and  it  is  not  pre- 
cipitated by  alum.  For  this  reason  its  retention  is  very  low, 
being  probably  only  that  amount  which  clings  to  the  surface  of 
the  fibres  from  the  very  dilute  solution  in  the  beater.  (  Its  low 
retention  was  proved  in  one  experiment  where  2  per  cent  was 
added  to  the  stock  in  the  beater  and  yet  the  paper  made  from 
it  failed  to  show  its  presence  when  tested  by  all  ordinary 
methods. 

It  is  asserted  by  many  of  the  older  paper  makers  that  by  the 
use  of  glue  in  the  beater  they  can  obtain  results  which  they  can 
get  in  no  other  way.  Its  use  is,  however,  costly  and  its  effects  are 
probably  greatly  over-rated. 

Viscose.  This  material,  which  is  a  solution  of  cellulose  pre- 
pared by  means  of  caustic  soda  and  carbon  bisulphide,  was  at 
one  time  proposed  for  engine  sizing.  The  solution  was  added  to 
the  beater  and  the  cellulose  regenerated  by  the  subsequent  addi- 
tion of  magnesium  sulphate  or  alum.  Theoretically  the  sizing 
of  a  paper  by  filling  its  pores  with  a  substance  of  the  same  chemi- 
cal composition  as  the  fibres  composing  the  sheet  is  a  very  attrac- 
tive proposition.  Practically,  however,  the  process  has  never 
attained  any  wide  application,  probably  because  of  the  some- 
what complicated  nature  of  the  chemical  reactions;  because  it 


288  SIZING 

charges  the  engine  with  certain  undesirable  chemicals;  and 
because  of  its  cost. 

This  process  also  does  not  size  by  making  water  resistant,  as 
does  rosin,  but  its  action  is  more  in  the  nature  of  the  starch  sizing 
of  textile  goods. 

<YjRubber  Resins.  These  resins  which  are  obtained  as  a  by 
product  from  the  treatment  of  certain  grades  of  rubber  have  been 
suggested  as  of  possible  use  in  sizing  paper.  As  they  are  unsa- 
ponifiable  they  cannot  be  dissolved  in  alkaline  solutions  and  hence 
can  only  be  used  to  replace  the  free  rosin  in  the  size.  "By  this 
means  they  are  dissolved  and  held  in  suspension  and  thus  may 
be  added  to  the  beater  just  as  is  ordinary  size.  Experiments  in 
German  mills  have  indicated  that  this  material  has  very  little 
value  but  our  own  tests  give  contrary  results  and  seem  to 
show  that  it  has  more  sizing  value  than  an  equal  amount  of 
colophony. 

If  this  material  ever  comes  on  the  market  in  sufficient  quan- 
tity to  compete  in  price  with  rosin  it  is  certainly  worthy  of  further 
investigation. 

The  Mitscherlich  Sizing  Process.  Among  the  substances 
occurring  in  waste  sulphite  liquor  are  compounds  derived  from 
the  wood  which  are  sufficiently  like  tannic  acid  to  possess  its 
power  of  precipitating  gelatine.  This  property  has  been  utilized 
by  Dr.  Mitscherlich  as  the  basis  for  an  engine  sizing  process 
which  is  conducted  as  follows :  Ordinary  glue  is  digested  at  60°  C. 
with  about  ten  times  its  weight  of  waste  sulphite  liquor.  After 
^several  hours,  during  which  time  the  mixture  should  be  stirred 
occasionally,  the  glue  is  dissolved  and  the  solution  is  then  diluted 
with  more  waste  liquor  until  it  is  present  to  the  extent  of  fifty 
times  the  weight  of  the  glue.  This  dilution  should  be  conducted 
at  ordinary  room  temperatures  and  should  be  made  very  grad- 
ually and  with  constant  stirring.  The  whole  is  allowed  to  stand 
for  twenty-four  hours  to  allow  the  flocculent  precipitate  to  settle, 
the  clear  liquor  is  then  decanted  and  the  precipitate  diluted  with 
a  quantity  of  water  equal  to  about  fifty  times  the  weight  of  the 
original  glue.  A  little  alkali  is  next  added  to  neutralize  the  free 


THE  MITSCHERLICH  SIZING  PROCESS  289 

acid  and  to  dissolve  the  compound  of  glue  and  astringent  material 
and  the  solution  so  prepared  is  then  ready  to  add  to  the  engine. 
Alum,  or  an  acid,  causes  the  re-precipitation  of  the  flocculent 
gelatine  compound  which  adheres  to  the  fibres  and  imparts  to 
them  its  sizing  properties.  ^This  process  has  never  met  with 
very  wide  application."7 


CHAPTER  X 
LOADING  AND  FILLING  MATERIALS 

Nearly  all  classes  of  papers,  except  a  few  for  special  purposes, 
contain  some  mineral  filling  or  loading  material  and  unless  it  is 
used  to  an  excessive  extent  it  cannot  be  considered  an  adulterant. 
In  fact  without  some  filler  it  is  impossible  to  produce  many  of 
the  grades  which  modern  printing  practices  demand,  since  it  fills 
up  the  interstices  between  the  fibres  and  gives  a  better  surface 
for  process  cuts  and  half-tones  which  are  so  largely  used.  It  also 
makes  the  paper  more  opaque,  improves  the  feel,  and  enables 
it  to  take  a  better  finish  on  calendering,  all  of  which  are  of 
importance  to  the  trade. 

Fillers  tend  to  increase  the  weight  more  than  the  bulk  of  the 
paper  and  therefore  cannot  be  largely  used  in  light,  bulky  papers 
such  as  the  so-called  " featherweights."  On  the  other  hand, 
when  they  are  used  in  very  large  amounts,  and  the  paper  subjected 
to  supercalendering,  they  are  of  great  assistance  in  producing 
the  effects  desired  in  imitation  coated  papers.  When  a  filler  is 
used  in  large  amount  it  quite  seriously  reduces  the  strength  of 
the  paper  produced;  hence  when  the  strength  of  a  paper  is 
specified,  and  a  filler  is  used,  a  better  grade  of  fibrous  stock  must 
be  employed  and  more  care  used  in  manufacturing  than  if  no 
filler  were  used.  This  has  been  amply  demonstrated  in  Ger- 
many where  in  1904,  at  the  instigation  of  the  Royal  Testing 
Office,  the  restrictions  as  to  amount  of  ash  in  the  various  classes 
of  papers  were  abolished.  Since  that  time  it  has  been  found  that 
the  requirements  for  strength  have  sufficed  to  keep  the  percentage 
of  ash  very  largely  within  the  limits  formerly  prescribed.  The 
amount  of  filler  also  has  a  notable  effect  on  the  sizing,  for  as  the 
percentage  of  ash  in  the  paper  rises  the  sizing,  as  shown  by  the 

290 


LOADING  AND   FILLING  MATERIALS 


291 


time  required  for  writing  ink  to  penetrate  the  paper,  decreases. 
This  is  well  illustrated  by  the  curves  in  Fig.  36,  which  show 
the  percentage  of  ash  and  the  sizing  tests  on  a  large  number  bf 
samples  taken  from  the  same  run  of  paper. 

The  materials  commonly  used  as  fillers  are  china  clay,  talc, 
asbestine,  calcium  sulphate  in  its  various  forms,  heavy  spar, 


20 
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Roll  Nos. 
FIG.  36.    EFFECT  OF  FILLER  ON  SIZING 

blanc  fixe  and  precipitated  chalk.  Many  of  these  are  sold  under 
trade  or  fancy  names  and  frequently  at  prices  which  do  not 
correspond  to  their  actual  value.  In  addition  to  these,  certain 
colors,  as  ochre,  lead  chromate,  ultramarine,  etc.,  are  sometimes 
used  in  sufficient  quantity  to  affect  the  bulk  and  ash  of  the  paper, 
but  as  these  are  used  primarily  for  coloring,  and  their  loading 
effect  is  merely  incidental,  they  will  not  be  considered  here. 


2Q2  LOADING  AND  FILLING  MATERIALS 

The  qualities  to  be  considered  in  judging  a  filler  are  color, 
fineness,  absence  of  grit,  mica,  etc.,  solubility,  specific  gravity  and 
chemical  composition.  The  chemical  analysis  of  a  filler,  as  a 
means  of  checking  individual  shipments  of  the  same  material, 
is  of  little  value,  except  in  special  cases  where  for  some  reason  a 
certain  constituent  must  be  proved  absent,  or  else  present  in 
definite  amount.  It  is  essential,  however,  to  know  the  chemical 
composition  of  the  various  fillers,  as  this  makes  it  possible  to  tell 
from  the  analysis  of  a  paper  ash  what  kind  of  filler  was  used,  and 
it  is  also  necessary  if  it  is  desired  to  know  the  amount  of  filler  in 
the  paper,  as  many  fillers,  on  igniting  the  paper  to  an  ash,  lose 
water  which  would  normally  be  retained  by  them  in  the  finished 
paper.  The  specific  gravity  is  of  importance,  as  it  shows  how 
the  filler  will  affect  the  bulk  of  the  paper,  while  the  presence  of 
grit  in  any  considerable  amount  indicates  that  the  wires,  felts 
and  jackets  will  be  subjected  to  unnecessary  wear  and  that  the 
paper  may  be  defective  to  such  an  extent  as  to  cause  serious 
trouble  in  printing.  When  making  heavily  colored  papers  in 
which  soluble  dyes  are  used,  the  type  of  filler  should  be  selected 
only  after  consideration  of  the  dye  to  be  used,  for  different  fillers 
have  different  absorptive  capacities  for  the  various  dyes.  Proper 
selection  of  the  filler  will  therefore  be  of  considerable  assistance 
in  obtaining  satisfactory  absorption  of  the  dye  and  in  reducing 
its  loss.  The  relation  of  fillers  to  dyes  will  be  discussed  in 
Chapter  XI. 

The  proportion  of  the  filler  added  to  the  engine  which  appears 
in  the  finished  paper  is  spoken  of  as  the  retention.  This  may 
vary  from  30  to  90  per  cent,  though  the  latter  figure  is  only 
reached  under  very  exceptional  circumstances  and  a  retention  of 
50  per  cent  is  generally  considered  satisfactory.  Many  factors, 
other  than  the  filler,  influence  its  retention  and  it  is  impossible 
to  estimate  their  effects,  except  in  a  general  way.  The  kind  of 
stock  and  the  extent  of  its  beating,  the  speed  of  the  paper  machine, 
the  pull  on  the  suction  boxes,  the  amount  of  filler  added  and 
the  thickness  of  the  sheet  must  all  be  taken  into  consideration. 
Slow  or  " greasy"  stock,  a  light  suction  and  a  thick  sheet  all 


RETENTION  OF  FILLERS  293 

tend  to  give  high  retention,  while  in  the  case  of  sulphate  of  cal- 
cium the  retention  increases  with  the  amount  added. 

A  study  of  the  loss  of  filler  taking  place  at  different  parts  of 
the  paper  machine  was  made  in  a  German  mill l  during  the 
running  of  a  rotary  press  print  paper  of  50  grams  per  square 
meter,  made  from  stock  containing  25  per  cent  sulphite  and  75  per 
cent  ground  wood.  The  ash  in  the  air  dry  stock  at  various 
points  was  as  follows: 

Per  cent 

Stock  from  the  chest 20.  o 

Stock  just  before  suction  boxes 19.  o 

Stock  after  the  couch 15.0 

Stock  after  first  press 14.  o 

Stock  after  second  press 13.5 

Finished  paper 13.0 

The  apparently  slight  loss  in  the  drainage  through  the  wire  is 
due  to  the  fact  that  the  white  water  was  used  over  again  and  the 
ash  in  the  stock  actually  flowing  onto  the  wire  would  therefore 
be  greater  than  that  in  the  chest. 

Working  with  sulphite,  and  with  sulphite  and  soda  furnishes, 
Kress  and  McNaughton 2  found  the  retention  to  decrease  slightly 
as  the  amount  of  clay  added  was  increased.  This  is  contra- 
dictory to  the  results  given  in  the  subjoined  table  from  observa- 
tions by  the  author.  They  also  found,  as  would  be  expected, 
that  increasing  the  thickness  of  the  sheet  —  or  the  ream  weight  — 
increased  the  retention.  It  was  also  increased  as  the  amounts  of 
size  and  alum  were  increased,  and  by  greater  hydration  of  the 
stock  in  the  .beater. 

The  following  figures  from  tests  made  under  the  observation  of 
the  author  show  what  may  be  expected  from  various  fillers  when 
used  in  manufacturing  high  grade  book  papers. 

1  Paper:  1916,  Sept.  20,  p.  13,  from  Wochbl.  Papierfabr. 

2  Kress  and  McNaughton:  Paper,  Oct.  3,  1917. 


2Q4 


LOADING  AND  FILLING  MATERIALS 


*  Filler 

Percentage  in  finished 
paper 

Percentage  retention 

China  clay  

2Q     I 

76    2 

•22    2 

74    6 

<          « 

26    7 

68  6 

<          <  < 

2<    6 

66  5 

<          <  < 

I  r    i 

^7    6 

Precipitated  chalk  

24    8 

38  7 

I9.I 
12    O 

40.9 
16  6 

«                « 

97 

<\4    O 

Asbestine 

22    "? 

72    4 

IO    8 

46    I 

« 

IO    2 

^2   4 

Pearl  finish  

24    Q 

64  4 

Crown  filler  

24    2 

t;i  2 

Blanc  fixe  

27    Q 

3Q  O 

Clay.  Clay  is  a  soft,  friable,  sectile,  white  substance  showing 
irregularly  shaped  particles  under  the  microscope  and  possessing 
only  a  moderate  plasticity  when  mixed  with  water.  It  is  a 
mixture  of  hydrated  silicates  of  alumina  containing  particles  of 
quartz,  mica  and  felspar  and  its  chemical  composition  is  approx- 
imately Al2O3-2Si02*2H20.  It  is  formed  by  the  weathering 
of  felspathic  minerals  and  the  presence  of  mica  indicates  its 
granitic  origin.  Those  clays  which  remain  overlying  the  rock 
from  which  they  were  formed  are  known  as  residual,  while  those 
which  have  been  conveyed  to  a  distance  by  eroding  influences 
are  called  sedimentary.  The  former  are  usually  more  free,  from 
iron  and  of  better  color  than  the  latter.  Good  grades  of  clay 
are  found  in  England,  France,  Bohemia  and  the  United  States, 
but  in  spite  of  our  own  deposits  the  greater  part  of  that  used  in 
this  country  is  still  imported.  This  is  probably  due  in  large  part 
to  insufficient  care  or  improper  methods  of  preparation,  and  it  is 
thought  that  these  will  shortly  be  overcome  so  that  domestic 
clays  will  play  a  much  more  important  part  in  American  manu- 
facture. 

Clay  is  prepared  for  the  market  by  washing  it  with  a  stream 
of  water  through  long  sluices  of  riffles,  in  which  the  sand  and 
mica  are  caught,  into  tanks  or  basins  in  which  the  fine  clay  is 


CLAY 


295 


allowed  to  settle.  The  water  is  then  drawn  off  and  the  clay  dug 
out  and  dried  when  it  is  ready  for  market.  Instead  of  these 
crude  methods  the  fine  clay  and  water  is  sometimes  passed 
through  filter  presses,  and  there  has  recently  been  proposed  an 
electrolytic  method  of  purification  and  separation  which  is 
claimed  to  give  a  product  perfectly  free  from  grit  and  much 
dryer  than  that  from  any  filter  press.  Even  the  very  finest 
washed  clays  contain  a  small  proportion  of  sand  and  mica  and 
there  is  always  some  moisture  present.  For  English  clays  up  to 
12  per  cent  is  permissible  though  it  more  frequently  runs  under 
than  over  that  figure.  It  is  not  well  to  have  a  clay  too  dry  as  it 
causes  loss  in  handling  and  the  dust  is  bad  from  a  hygienic 
standpoint.  Freezing  moist  clay  causes  no  permanent  change 
in  composition  or  physical  properties  so  that  clay  which  has 
been  frozen  can  be  used  with  perfect  safety  after  it  has  been 
thawed  out. 

The  following  analyses  give  a  good  idea  of  the  composition  of 
different  grades  of  clays;  numbers  one  to  four  being  English  clays 
tested  by  Remington  1  while  five  and  six  are  American  clays. 


No.  of  clay 

i 

2 

3 

4 

5 

6 

Used  for 

High 

News 

White 

papers 

printings 

Silica,  SiO2  
Alumina,  AlzOs  
Ferric  oxide,  Fe2O3.  .  . 
Lime,  CaO  

46.21 
39-82 
0.38 
0.45 

47.60 
38.26 

o-55 

0.42 

46.46 

37-40 
2.OO 

0.86 

45-92 
38.43 
0.71 
1.18 

45-67 
37.86 
1.48 
O.O5 

43-36 
40.54 
0.90 
0.08 

Magnesia,  MgO  
Alkalis,  K2O  
Total  water  

O.IO 

0.23 

12.  8l 

0.20 

0-57 
12  .40 

0.21 

1.26 

11.81 

0.21 
0.78 
12.77 

O.OI 

0.80 
13.22 

0.38 

0.88 
13.86 

Grit  per  cent  

IOO.OO 

0.09 

IOO.OO 
0.32 

100.00 
2.22 

100.00 

2.28 

99-09 

IOO.OO 

The  similarity  of  these  analyses  is  quite  noteworthy  and  it  is 
evident  that,  apart  from  the  ferric  oxide  which  seriously  influences 


J.  Ind.  Eng.  Chem.,  3,  555. 


296 


LOADING  AND   FILLING  MATERIALS 


the  color,  the  qualities  by  which  a  clay  may  be  judged  are  largely 
physical.  It  is  stated  by  one  authority  that  if  the  grit  rises  over 
2  per  cent  the  clay  would  be  objectionable  for  high  grade  news- 
paper. 

The  total  water  in  these  clays  is  very  largely  that  chemically 
combined.  This  is  not  driven  off  on  drying  at  100°  C.  but  is 
expelled  at  a  red  heat  or  at  the  temperature  of  the  usual  ash 
determination.  For  this  reason  the  percentage  of  ash  as  deter- 
mined in  a  paper  loaded  with  clay  should  be  divided  by  0.88  in 
order  to  convert  the  ash  into  the  approximate  amount  of  actual 
filler;  this  is  neglecting  the  ash  from  the  fibrous  materials  and 
from  the  size  and  alum  which  is  usually  insignificant  in  compar- 
ison with  the  filler.  Clay  loses  all  hygroscopic  moisture  at 
1 00°  C.  and  all  combined  water  at  about  500°  C.  Clay  which 
has  been  dried  at  100°  regains  its  plasticity  on  soaking  in  water. 
In  this  connection  it  should  be  noted  that  some  air  dry  clays 
contain  a  small  amount  of  moisture  which  is  driven  off  on  drying 
at  100°  C.  and  again  absorbed  on  exposure  to  the  atmosphere. 
In  a  number  of  high  grade  clays  this  moisture  was  found  to 
amount  to  0.43  to  0.77  per  cent  of  the  weight  of  the  air  dry 
clay. 

The  size  of  particles  varies  greatly  in  different  clays  and  the 
proportion  of  coarse  and  fine  particles  may  be  quite  different  in 
clays  which  are  very  similar  in  appearance.  Tests  of  a  number 
of  clays  by  separation  of  the  particles  which  settle  ij  ins.  in 
different  lengths  of  time  gave  the  following  results: 


Domestic 

UXL 

GAG 

GH 

AR 

Settling  in    i  minute  

Per  cent 
2 

Percent 
4 

Percent 
26 

Percent 
13 

Percent 
44 

"         "     i-io    minutes  

2O 

24 

IO 

2C 

2C 

"  10-120        " 

•JQ 

37 

28 

2C 

12 

"         "  over  2  hours 

48 

sir 

36 

27 

IQ 

In  the  case  of  UXL  clay  the  sizes  of  the  particles  separated  in 
this  way  were  found  to  be 


PLATE  27 

Domestic  Filler  Clay.    Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


*---V\\ 


r.'A 


•>'•'•  WSS^SK^^' 

.••-;•   •:*;.*     '  /.-«:"•!&'',•'?  -  -  •."*'•'  •' 

lliS^  8 


"•  .«< 


PLATE  28 

English  Coating  Clay.    Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


CLAY  297 

Settling  in  i  minute o.  028  m.m. 

i-io  minutes o.  007-0. 018  m.m. 

10-120  minutes 0.0035-0.007  m.m. 

over  2  hours o.  0015  m.m. 

The  specific  gravity  of  clay  is  variously  given  as  2  to  2.86. 
Observations  by  the  author  on  six  different  samples  of  thoroughly 
dried  English  clays  showed  them  to  range  from  2.568  to  2.634. 
The  weight  per  cubic  foot  of  clay  as  ordinarily  received  varies 
according  to  the  method  of  handling  from  53  Ibs.  when  the  fine 
material  is  run  in  loosely  to  84  Ibs.  when  the  clay  is  tamped  in 
hard.  This  is  for  clay  with  about  7.5  per  cent  of  moisture. 

Clay  is  r  ^lly  added  to  the  stock  in  the  beater  soon  after  it  is 

furnished  s    thatjt  may  be  well  distributed  before  the  alum  is 

added.     TJie  old  way  was  to  add  the  dry  clay  direct  to  the 

beater  but  the  more  progressive  mills  are  now  mixing  the  clay 

with  water  and  straining  before  adding  to  the  stock,  thus  avoid- 

ST  rnvrh  dirt.     In  preparing  domestic  clays  for  use  in  this  way 

aonia  or  sodium  phosphate  is  sometimes  found  to  be 

'si&nce  in  helping  the  clay  to  work  up  and  in  keeping 

vision.     In  testing  this  clay  mixture  for  uniformity 

.xd  be  noted  that  the  consistency  of  a  clay- water  mixture 

^endent  on  the  physical  qualities  of  the  clay  as  well  as  upon 

'••"  -junt  used.     Of  six  clays  which  were  mixed  in  such  a 

it  loo  c.c.  of  the  mixture  contained  from  19.6  to  19.9 

;f  dry  clay  the  Baume  readings  varied  from  16.5°  to  23° 

fc,Aju        fe  i;hat  this  method  cannot  be  used  for  daily  control  if  the 

clay  supply  varies. 

A  satisfactory  control  test  for  the  clay  mixture  supplied  to 
the  beaters  may  be  made  by  determining  the  weight  of  a  definite 
volum _:  of  the  mixture  in  comparison  with  an  equal  volume  of 
water.  A  250  c.c.,  glass  stoppered,  ungraduated  flask  is  a  con- 
venient volume  to  use.  First  clean,  dry  and  weigh  the  empty 
flask  including  the  stopper;  then  fill  it  completely  with  distilled 
water,  insert  the  stopper  carefully  so  that  no  air  is  trapped,  dry 
the  outside  of  the  flask  and  weigh  again.  Once  these  two 
weights  are  established  for  a  given  flask  they  may  be  consid- 


298  LOADING  AND   FILLING  MATERIAL 

ered  as  constants.  The  test  therefore  consists  simply  in  filling 
the  flask  with  the  clay  mixture,  cleaning  the  outside,  especially 
around  the  stopper,  and  weighing. 

Assuming  the  specific  gravity  of  clay  to  be  2.6  the  calculation 
of  the  weight  of  dry  clay  in  the  flask  would  be  as  follows: 

Let     x  =  weight  of  dry  clay  in  flask 
y  =  weight  of  water  in  flask 
w  =  weight  in  grams  of  flask  full  of  clay  mixture 
c  =  capacity  of  flask  in  cubic  centimeters  =  weight  of 

water  it  will  hold 
/  =  weight  of  empty  flask  in  grams. 

Then  x  =  w  —  f  —  y 

x 
~^6 

x  =w  -f-c+JL 

2.6 

_  2.6  (w  —  /)  —  2.6  c 
1.6 

x  =  1.625  w  —  1.625  (/  +  c)- 

Since  /  and  c  are  constants  it  is  only  necessary  to  make  a 
single  weighing  of  the  flask  full  of  clay  mixture  in  order  to  be 
able  to  calculate  the  amount  of  dry  clay  it  contains.  This  can 
be  converted  readily  into  pounds  per  inch  in  any  measuring 
tank  which  may  be  used. 

This  method  of  testing  has  been  employed  in  mill  control 
work  for  a  number  of  years  and  if  the  flask  is  weighed  to  a  tenth 
of  a  gram  the  results  are  found  to  check  closely  with  those  ob- 
tained by  drying  and  weighing  a  definite  volume  of  the  clay 
mixture. 

Gypsum.  This  is  a  natural  calcium  sulphate,  CaS04  •  2  H2O, 
and  is  prepared  for  use  as  a  filler  by  grinding,  or  it  may  be  cal- 
cined, finely  ground,  washed  and  dried  quickly  to  prevent  its 
reabsorbing  water  and  becoming  hard  and  compact.  The  ground, 


PEARL  HARDENING  299 

uncalcined  mineral  has  the  form  of  plates.  Three-quarters  of 
the  water  of  crystallization  of  gypsum  is  driven  off  at  a  tem- 
perature of  120°  C.  and  the  calcined  gypsum  which  is  formed 
takes  up  water  readily  and  sets  to  a  firm  mass.  If,  however, 
the  gypsum  is  heated  to  over  160°  C.  there  is  formed  an  an- 
hydride which  absorbs  water  very  slowly  and  hence  may  be 
rapidly  washed.  This  anhydride  on  long  soaking  in  water 
changes  in  form  from  the  irregular  particles  of  the  ground 
mineral  to  small  needle-shaped  crystals.  This  change  takes 
place  so  slowly  that  it  is  doubtful  if  it  is  completed  during  the 
time  elapsing  between  the  furnishing  of  the  engine  and  the 
running  of  the  stock  into  paper. 

Gypsum  is  generally  added  directly  to  the  beating  engine  and 
results  in  the  production  of  rather  soft  paper.  Its  use  also  tends 
to  fill  up  the  felts  due  to  the  crystallization  of  CaSO4  •  2H2O. 
All  gypsum  is  soluble  in  hydrochloric  acid,  or  in  400  to  500 
parts  of  water,  which  causes  serious  loss  and  poor  retention 
unless  the  back-water  is  used  over  again.  This  solubility  has 
not  been  found  to  interfere  in  any  way  with  the  rosin  sizing  in 
the  engine  in  which  it  is  used  and  in  certain  cases  it  is  even 
claimed  to  be  beneficial.  The  loss  on  ignition  of  calcined  gyp- 
sum is  only  0.5  to  2  per  cent,  while  that  of  the  uncalcined  mate- 
rial is  nearly  21  per  cent. 

Pearl  Hardening  is  an  artificial,  hydra  ted  calcium  sulphate 
made  by  precipitating  a  solution  of  calcium  chloride  with  sodium 
sulphate.  It  may  occur  in  two  forms,  flat,  tabular  crystals  or 
minute,  needle-shaped  crystals.  Its  specific  gravity  is  2.39  and 
it  loses  21  per  cent  of  its  weight  on  ignition.  Other  names 
for  calcium  sulphate  preparations,  either  hydra  ted  or  anhy- 
drous, are  Pearl  White,  Crown  Filler,  Pearl  Finish,  Annaline, 
Alabastine,  etc.  Some  of  these  contain  considerable  water  be- 
sides that  chemically  combined,  and  extravagant  claims  are  fre- 
quently made  as  to  their  advantages  both  as  to  the  finish 
imparted  to  the  paper  and  the  amount  retained.  These  claims 
are  to  be  taken  with  a  grain  of  salt  as  all  possess  essentially  the 
properties  of  gypsum  or  pearl  hardening. 


300  LOADING  AND   FILLING  MATERIALS 

Precipitated  Chalk  or  calcium  carbonate  is  occasionally  used 
as  a  filler  particularly  in  very  thin  papers  of  the  Bible  class  such 
as  are  now  used  so  largely  for  the  printing  of  dictionaries  and 
encyclopaedias.  It  may  be  added  directly  to  the  engine  but 
much  better  results  are  obtained  by  mixing  a  solution  of  cal- 
cium chloride  with  the  stock  and,  when  it  has  become  thoroughly 
incorporated,  precipitating  it  with  a  solution  of  sodium  car- 
bonate. Care  should  be  taken  that  the  quantities  used  are 
approximately  equivalent  as  otherwise  serious  losses  may  occur; 
a  slight  excess  of  either  one  has  not,  however,  been  found  to  be 
injurious  to  the  paper  though  a  large  excess  of  calcium  chloride 
would  cause  it  to  absorb  moisture  and  become  limp  and  lifeless. 

Calcium  carbonate  seriously  interferes  with  the  rosin  sizing 
and  even  when  the  size  is  precipitated  by  alum  before  the  filler 
is  added  it  has  been  found  practically  impossible  to  produce  a 
well-sized  sheet.  The  advantage  of  precipitated  chalk  lies 
largely  in  its  color  since  it  imparts  to  the  paper  a  much  whiter 
color  than  can  be  obtained  by  the  use  of  clay.  It  also  gives 
the  paper  a  characteristic  velvety  feel  though  it  does  not  take 
such  a  high  polish  on  supercalendering  as  does  a  clay-filled 
paper. 

Talc.  Talcum  or  Spanish  chalk  is  a  hydrated  silicate  of 
magnesium.  A  part  of  the  magnesia  is  nearly  always  replaced 
by  alumina  so  that  it  may  be  regarded  as  a  double  silicate  of 
magnesium  and  aluminum  with  the  magnesium  largely  in  ex- 
cess. It  is  very  soft,  has  a  characteristic  soapy  or  greasy  feel 
and  is  usually  of  a  creamy  or  greenish  white  shade.  Its  specific 
gravity  is  2.6  to  2.9.  It  is  very  resistant  to  acids  and  solutions 
of  alkalis  and  also  to  heat,  losing  no  water  below  a  red  heat. 
In  preparing  it  for  the  market  the  stone  is  sorted  according  to 
color  and  then  ground  and  graded  either  by  an  air  blast  or  by 
bolting.  The  product  is  not  so  fine  as  clay  and  the  grit  is  usu- 
ally greater.  It  is  often  adulterated  with  heavy  spar  or  more 
often  with  ground  limestone. 

Talc  improves  the  printing  qualities  and  the  feel  of  the  paper 
and  gives  it  a  rag-like  appearance.  It  is  said  that  20  per  cent 


PLATE  29 

Crown  Filler.    Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


PLATE  30 

Talc.    Magnification  100  diameters.     Photographed  by 
Bureau  of  Standards. 


PLATE  31 

Asbestine.     Magnification  100  diameters.    Photographed  by 
Bureau  of  Standards. 


HEAVY  SPAR  AND   WITHERITE 


301 


of  talc  will  give  the  same  results  as  30  to  40  per  cent  of  lower 
grade  china  clay. 

Asbestine,  or  agalite,  is  a  fibrous  talc  which  occurs  as  an  alter- 
ation product  of  tremolite.  It  is  of  American  origin  and  is  ex- 
tensively prepared  in  St.  Lawrence  County,  N.  Y.  It  is  nearly 
pure  (95  to  97  per  cent)  magnesium  silicate  and  being  in  the 
form  of  rodlets  attaches  itself  well  to  the  fibres  and  gives  good 
retention.  It  does  not  impart  quite  so  high  a  finish  to  the 
paper  as  does  talc.  The  best  grades  are  free  from  sand,  nearly 
free  from  iron  and  almost  snow  white.  This  material  loses 
up  to  1.3  per  cent  on  drying  at  100°  C.  and  from  0.5  to  7  per  cent 
on  ignition.  The  following  analyses  are  fairly  representative  of 
the  composition  of  asbestine  or  agalite. 


• 

2 

3 

Silica,  SiO2  

60.59 

61.89 

62  .OI 

Alumina,  A^Os 

o  13 

i   36 

O    31 

Ferric  oxide,  Fe^Os 

O    23 

o  44 

O    IO 

Manganese  oxide,  MnO  

1.16 

Calcium  oxide,  CaO  

4.21 

Magnesia,  MgO  
Water  

34.72 

3-77 

30.70 
i  .40 

32.12 

4-30 

100.60 

IOO.OO 

98.84 

Heavy  Spar  and  Witherite  are  sometimes  used  as  fillers.  The 
former  is  a  naturally  occurring  barium  sulphate,  BaSO,*,  while 
the  latter  is  carbonate  of  barium,  BaCO3.  In  preparing  the 
heavy  spar  the  foreign  stone  is  broken  off  and  the  spar  is  first 
ground  dry,  then  wet  and  finally  washed. 

Neither  of  these  materials  is  very  satisfactory  as  their  high 
specific  gravity,  4.2  to  4.5,  causes  much  loss  of  filler  and  also 
settling  on  the  wire  so  that  the  two  sides  of  the  sheet  are  not 
alike  and  the  wire  side  is  particularly  destructive  to  pens  and 
type.  If  barium  sulphate  is  to  be  used  as  a  filler  it  should  be 
precipitated  in  the  engine  by  adding  first  barium  chloride  and 
then  a  solution  of  sodium  sulphate  and  great  care  should  be 
exercised  that  loss  does  not  occur  through  an  insufficiency  of 
the  latter. 


302 


LOADING  AND   FILLING  MATERIAL 


Testing  Fillers.  The  color  of  fillers  is  best  determined  by 
comparison  with  standard  samples  of  similar  materials.  As  the 
moisture  present  has  a  very  great  influence  on  the  color,  espe- 
cially with  clays,  the  materials  compared  should  be  equally 
dry.  This  is  readily  assured  by  drying  at  100°  C.  before 
comparing.  One  method,  which  is  extensively  used,  is  to  mix 
the  material  to  a  paste  with  water  on  a  glass  plate  and  after 
drying  to  compare  with  the  standard,  similarly  treated.  A  bet- 
ter method  and  one  which  can  be  rapidly  carried  out  is  to  use  a 
block  of  wood  in  the  top  of  which  there  are  shallow  compart- 
ments separated  by  knife  edges 
coming  flush  with  the  upper  sur- 
face of  the  block.  Such  a  test- 
ing block  is  shown  in  Fig.  37. 
Into  one  of  these  compartments 
the  standard  material  is  pressed 
by  means  of  a  polished  steel 
spatula  and  in  the  next  the  filler 
to  be  compared  is  placed.  The 
knife  edges  permit  of  very  close 
contact  of  the  two  samples,  the 
polished  spatula  gives  a  good 

surface  and  the  small  size  of  the  block  allows  it  to  be  easily 
handled  so  that  it  may  be  held  in  any  position  with  regard  to 
the  light  and  the  samples  examined  from  all  sides. 

In  many  cases  it  is  well  to  note  how  much  a  filler  can  be  im- 
proved by  the  addition  of  blue.  This  may  be  readily  done  by 
grinding  the  dry  filler  in  a  mortar  with  a  very  little  ultramarine 
and  then  comparing  the  color  with  the  same  material  unblued 
or  with  the  standard. 

To  determine  whether  a  clay  has  been  blued,  it  may  be  moist- 
ened with  turpentine  to  form  a  rather  thin  paste  on  a  porcelain 
plate,  and  then  compared  with  samples  which  are  known  to  be 
blued  and  unblued  and  which  have  been  treated  in  the  same 
manner.  The  artificially  colored  clays  are  said  to  give  a  bluish 
green  color  but  as  it  is  claimed  there  are  a  number  of  natural 


FIG.  37.    BLOCK  FOR  TESTING  COLOR 
OF  CLAYS 


TESTING  FILLERS  303 

English  clays  which  give  this  same  color  with  turpentine  the 
test  cannot  be  considered  as  conclusive. 

A  better  method  is  carried  out  as  follows:  In  one  of  two 
similar  white  porcelain  dishes  place  a  measured  amount  of 
freshly  prepared  saturated  lime  water  and  in  the  other  dish  an 
equal  amount  of  distilled  water.  Then  into  each  of  these  liquids 
dust,  from  the  end  of  a  knife  or  spatula,  a  little  at  a  time,  equal 
amounts  of  the  clay.  After  allowing  to  stand  for  a  few  minutes 
the  excess  liquid  should  be  siphoned  off  and  the  moist  clay 
examined.  If  the  clay  has  been  artificially  blued  the  lime  water 
will  remove  the  bluing  so  that  the  two  samples  will  appear 
quite  different  after  this  treatment.  Although  neither  of  these 
tests  is  entirely  satisfactory,  yet  if  both  are  applied  it  is  possible 
to  get  a  fairly  accurate  idea  whether  the  sample  has  been  arti- 
ficially blued  or  not. 

The  grit  in  clay  or  other  loading  material  may  be  determined 
in  a  number  of  ways.  One  roughly  quantitative  test  is  to  place 
a  little  of  the  clay  in  the  mouth  when  the  grit  may  be  readily 
detected  between  the  teeth.  A  more  accurate  procedure  and 
one  which  may  be  easily  duplicated  by  independent  operators 
is  to  weigh  out  a  sample  of  the  clay,  place  it  on  a  standard  mesh 
screen  and  wash  it  with  a  spray  of  water  until  the  water  running 
away  is  perfectly  clear.  The  residue  on  the  screen  is  then 
dried,  weighed,  and  reported  as  grit.  The  size  of  the  sample 
may  be  varied  according  to  the  preference  of  the  operator  but 
20  grams  has  been  found  to  be  a  convenient  amount.  Some 
form  of  spray  head  which  delivers  a  fine  spray  under  a  consid- 
erable pressure  will  be  found  very  satisfactory  for  washing  the 
clay  on  the  screen.  It  is  also  desirable  to  make  the  test  on 
both  2oo-mesh  and  3oo-mesh  screens  in  order  to  get  a  more 
comprehensive  idea  of  the  character  of  the  grit. 

A  flotation  process  which  gives  excellent  comparative  results 
may  be  carried  out  by  means  of  a  large,  wide  mouthed,  bottle 
fitted  with  an  inlet  tube  for  water  and  a  siphon  whose  inlet  is 
always  kept  near  the  surface  of  the  liquid  by  means  of  a  float. 
This  siphon  is  fitted  with  an  automatic  stop  to  prevent  its  en- 


304 


LOADING  AND   FILLING  MATERIALS 


tirely  emptying  the  bottle.  The  clay,  or  other  filler  to  be 
tested,  is  mixed  with  water  and  placed  in  the  bottle  and  water 
is  forced  in  rapidly  through  the  inlet  tube  until  it  rises  to  a 
mark  near  the  neck.  The  mixture  is  allowed  to  stand  a  definite 
time  and  the  siphon  then  started;  this  process  is  repeated  until 
at  the  end  of  the  settling  period  the  water  is  perfectly  clear  for  a 
definite  distance  down  from  the  filling  mark.  Any  material 
settling  more  than  this  distance  in  the  standard  time  is  con- 
sidered as  grit  and  its  quantity  is  determined  by  drying  and 
weighing.  It  is  evident  that  the  dimensions  of  this  apparatus 


-Tube  Support 


Siphon  Tube 


Hose 

C  on  ne  ct  ion — >• 


*  Water  Inlet 


!    ii 

\\J^RubberI 

\r      ^Connectic 

',!    !  !  - 

!]    || 

\ 

Jjl.^ 

<—  Glass  Receptacle 

ji  i  _x- 

•^  Graduations 

Hose  > 
Connection 

>-i-l 

2*  apart 

I 

^-Float         — 

FIG.  38.    APPARATUS  FOR  DETERMINING  GRIT  IN  FILLERS 

may  be  arranged  to  suit  the  convenience  of  the  operator  but 
those  of  an  outfit  which  gives  very  satisfactory  results  with 
clay,  blanc  fixe,  asbestine,  etc.,  are  shown  on  the  accompanying 
sketch,  Fig.  38.  This  method  cannot  be  employed  with  calcium 
sulphate  because  of  its  slight  solubility. 

The  grit,  when  separated  by  any  method,  should  be  examined 
by  means  of  the  microscope  as  its  appearance  reveals  much  as 
to  the  quality  of  the  filler  and  gives  some  idea  of  the  trouble 
it  is  apt  to  cause.  Thus  the  grit  from  clay  may  be  either  sand 
or  mica,  and,  while  the  former  causes  wear  on  the  wire  and  some- 
times pinholes  in  the  paper,  the  latter  may  make  shiny  spots 


TESTING  FILLERS  305 

which  are  apparent  on  looking  across  the  sheet  and  also  give 
trouble  in  printing. 

Talc,  as  stated  above,  is  often  adulterated  and  hence  its  color 
is  not  a  sure  criterion  of  value.  It  should  be  tested  for  gypsum, 
calcium  carbonate,  mica,  iron  and  sand.  The  usual  test  for 
calcium  carbonate  is  by  boiling  with  acid  and  noting  the  loss 
in  weight,  but  if  the  acid  used  is  too  strong  the  test  may  be 
erroneous  because  the  solvent  action  includes  other  portions  of 
the  filler.  Good  grades  of  talc  should  not  contain  over  i  to  2 
per  cent  of  oxides  of  iron  or  over  3  to  4  per  cent  of  CaCO3. 
Talc  may  be  readily  distinguished  from  clay  by  moistening  with 
a  little  cobalt  nitrate  solution  and  warming  over  a  flame;  the 
talc  gives  a  pinkish  color  and  the  clay  a  strong  blue. 


CHAPTER  XI 
COLORING 

The  importance  of  coloring  matter  to  the  paper  industry  is  not 
always  evident  to  the  casual  observer  but  it  is  at  once  realized 
when  it  is  understood  that  very  few  papers  are  made  without 
coloring  matter  of  some  kind.  This  is  of  course  self-evident  in 
the  case  of  heavily  colored  papers,  or  even  pronounced  shades,  but 
it  is  equally  true  of  white  papers,  for  very  few  of  these  are  made 
of  the  natural  color  of  the  fibre./  It  may  even  be  said  that  color- 
ing, as  applied  to  the  production  of  shades  of  white,  is  of  much 
more  importance  than  in  the  making  of  colored  specialities,  for 
the  production  of  the  former  runs  into  far  greater  tonnage.  It 
is  also  true  that  the  maintenance  of  uniformity  in  a  tinted  white 
requires  more  attention  and  care  than  in  the  case  of  deeper 
colored  papers,  for  a  slight  error  in  the  amount  of  color  used  will 
make  an  appreciable  difference  in  the  resulting  shade,  while  with 
deeper  colors  an  error  of  the  same  magnitude  will  have  hardly 
noticeable  results.  Variations  in  the  color  of  the  fibres  used  are 
also  much  more  serious  in  the  case  of  tints  than  they  are  with 
deeper  colors. 

In  coloring  paper  it  is  usually  required  that  the  shade  of  a 
sample  be  matched.  When  such  a  sample  is  submitted  previous 
runs  of  paper  should  be  looked  over  to  see  if  anything  of  the  same 
or  a  similar  color  has  been  made  before.  It  is  often  the  case 
that  the  records  of  former  orders  will  show  just  about  what 
coloring  matters  should  be  used  and  an  engine  can  then  be 
colored  up  and  the  paper  compar-ed  with  the  sample  as  soon  as 
it  gets  over  the  machine.  When  the  shade  desired  is  an  entirely 
new  one  the  use  of  a  small  beater,  of  a  pound  or  two  capacity, 
will  be  found  very  convenient.  By  using  a  weighed  amount  of 

306 


COLORING  307 

stock  in  such  a  beater,  sizing  and  loading  as  usual,  and  noting 
carefully  the  quantities  of  colors  used,  the  amounts  necessary  for 
the  larger  engines  may  be  easily  calculated.  The  stock  pre- 
pared in  the  small  beater  should  be  made  into  sheets  on  a  hand 
mould  and  dried  on  a  steam  heated  drying  cylinder.  The  sheets 
may  then  be  compared,  either  before  or  after  calendering,  with 
the  sample  submitted.  When  such  records  or  equipment  are 
not  available  a  small  part  of  the  sample  should  be  reduced  to  a 
pulp  with  a  little  water,  being  careful  not  to  use  so  much  that 
coloring  matter  is  lost  by  being  washed  out.  The  first  engine  is 
then  colored  up  to  match  this  wet  sample.  Whichever  of  these 
methods  is  used  a  sample  of  the  paper  should  be  taken  from  the 
winders,  as  soon  as  the  color  gets  thoroughly  over  the  machine, 
and  compared  with  the  sample  submitted.  If  the  shade  is  not 
right  then  the  proper  changes  should  be  made  at  once,  both 
in  the  stock  in  the  chest  and  in  the  other  engines  whicfy  are 
being  prepared. 

VJn  estimating  the  amount  of  dye  to  use  due  attention  must  be 
paid  to  the  beating  of  the  stock  and  the  calendering  of  the  finished 
paper.  The  more  hydrated  the  stock  has  become  from  prolonged 
beating  the  less  dye  will  be  required  for  a  given  shade.  Calen- 
dering and  supercalendering  also  darken  the  shade. 

When  a  colored  order  is  to  be  made  it  is  desirable  to  start  in 
the  morning  so  that  plenty  of  daylight  may  be  available  for  match- 
ing the  shade.  The  nature  of  the  light  used  for  color  compar- 
isons is  important  and  a  subdued  north  light  is  generally  con- 
sidered best.  This  should  be  from  a  window  not  affected  by 
reflections  from  neighboring  buildings.  Whatever  light  is 
selected  as  a  standard,  it  should  be  used  for  all  color  work  as  the 
same  results  cannot  be  obtained  if  south  light  is  used  one  day  and 
north  light  the  next.  Difficulties  from  variations  of  light  are 
entirely  avoided  if  one  of  the  color  matching  outfits,  or  so-called 
" daylight  lamps,"  is  used.  These  vary  more  or  less  in  quality 
but  several  excellent  ones  are  on  the  market.  To  give  the  best 
results  a  lamp  of  this  type  should  be  used  in  a  dark  room. 

In  comparing  colors  the  first  impression  should  be  decisive  as 


308  COLORING 

the  eye  becomes  less  sensitive  by  prolonged  staring.  If  doubt 
exists  after  the  first  glance  rest  the  eyes  by  closing  them,  or  by 
looking  at  some  distant  object,  and  then  make  a  second  com- 
parison. When  papers  are  being  examined  they  should  be 
folded  to  such  an  extent  that  then:  thickness  prevents  any  light 
from  being  transmitted  through  them  since  it  is  the  light  reflected 
from  the  surface  which  it  is  desired  to  compare.  It  is  also  well 
to  change  the  samples  from  side  to  side  —  that  in  the  right  hand 
being  transferred  to  the  left,  and  vice  versa  —  since  the  relative 
positions  of  the  sheets  has  an  influence  on  their  apparent 
cojprs. 

[in  the  coloring  of  paper  the  materials  used  may  be  divided  into 
two  general  groups,  the  pigments,  which  are  for  the  most  part 
insoluble  materials,  and  the  dyes,  which  are  generally  employed 
in  solution.^  (Each  of  these  classes  has  certain  advantages  and 
disadvantages  which  must  be  taken  into  consideration  in  select- 
ing the  coloring  matter  to  be  used  in  any  particular  lot  of  paper. 

[Pigments.  Pigments  are  as  a  rule  very  fast  to  light  and  have 
the  added  advantage  that  they  increase  the  weight  of  the  paper 
by  acting  as  fillers.  They  are  not  generally  so  brilliant  as  the 
dyes  and  have  been  in  most  cases  replaced  by  the  latter.  They 
have  properties,  however,  which  make  them  valuable  for  certain 
papers  and  they  should  not  be  overlooked  because  they  are  more 
or  less  old  fashioned.  Both  pigments  and  paste  colors  may  with 
safety  be  added  directly  to  the  beater  though  heavy  colors  such 
as  the  canary  and  orange  pastes  may  advantageously  be  thinned 
with  a  little  water  to  prevent  the  settling  of  lumps  and  to  insure 
their  thorough  mixing  with  the  stock.  While  coloring  with 
pigments  is  a  purely  mechanical  operation  it  is  at  the  same  time 
necessary  to  pay  due  attention  to  the  nature  of  the  materials 
used  and  to  those  of  the  substances  with  which  they  come  in 
contact;  otherwise  trouble  will  be  caused  by  using  simultaneously 
substances  which  are  injurious  to  each  other. 

Natural  mineral  colors  are  obtained  from  numerous  natural 
deposits  but  before  being  of  value  they  must  be  ground  and 
separated  in  some  way  from  any  coarse  or  gritty  particles.  The 


PIGMENTS  309 


fineness  of  their  particles  never  equals  that  of  the  pigments  pro- 
duced by  chemical  means  but  the  finer  they  are  ground  the  better 
results  they  will  give.  In  addition  to  this  mechanical  treatment 
some  of  the  earth  colors  are  also  treated  chemically  and  in  some 
cases  various  shades  are  obtained  by  heating  the  colors  to  certain 
temperatures.  The  shades  of  the  natural  mineral  colors  are 
usually  of  a  subdued  rather  than  a  brilliant  nature  but  so  far  as 
permanence  is  concerned  they  are  not  equaled  by  any  other 
class  of  colors.  Among  colors  of  this  class  which  are  of  interest 
to  the  paper  maker  are  ochres,  and  red  and  brown  earth  colors. 
Whites^ which  would  also  come  in  this  class,  such  as  clay,  gypsum, 
blanc  fixe,  etc.,  are  discussed  in  the  chapter  on  fillers. 

Ochres  depend  for  their  coloring  power  upon  ferric  oxide  or 
hydrated  ferric  oxide,  and  various  shades  from  yellow  to  brown 
are  found  upon  the  market.  The  best  are  finely  divided  powders, 
soft  to  the  touch,  and  possessing  plastic  properties;  dark-colored 
brands  of  this  nature  are  generally  richest  in  coloring  matter. 
Ochres  are  sometimes  mixed,  or  "topped,"  with  chrome  yellow 
to  produce  more  brilliant  shades;  such  products  possess  the 
defects  of  chrome  yellow  and  if  used  without  proper  precautions  <- 
are  likely  to  cause  trouble. 

The  red  earths  owe  their  coloring  power  to  the  presence  of 
amorphous  ferric  oxide.  This  is  the  chief  ingredient  in  red  hem- 
atite, which  is  the  basis  for  numerous  colors.  Other  reds  are 
obtained  by  heating  to  redness,  clays  which  contain  hydrated 
ferric  oxide.  This  class  of  colors  includes  a  number  of  "red 
oxides,"  varying  from  yellowish  to  bluish  red,  and  also  Pompeian 
and  Venetian  reds  which  are  usually  of  less 'strength  than  the 
"oxides." 

Among  the  brown  earth  colors  are  "velvet,"  "umber"  and 
"chestnut"  brown  which  depend  upon  burnt  ferric  hydrate  for 
their  coloring  power.  True  umber  consists  mostly  of  manganese 
silicate  which  is  greenish  brown  in  its  natural  state  but  becomes 
a  rich  deep  brown  on  burning. 

These  natural  mineral  colors  are  largely  used  in  the  production 
of  wall  paper,  for  which  purpose  their  subdued  shades,  their  fast- 


310  COLORING 

ness  to  light  and  their  resistance  to  atmospheric  influences  render 
them  especially  suitable. 

Artificial  mineral  colors  are  still  used  quite  extensively  in  the 
coloring  of  paper,  though,  as  already  stated,  many  of  them  have 
been  replaced  by  aniline  dyes.  Among  those  which  are  still 
relatively  important  are  chrome  yellow,  Prussian  blue  and 
ultramarine. 

_  Chrome  yellow  may  be  obtained  in  the  paste  form  from  the 
manufacturers  of  pigments  or  it  may  be  prepared  directly  in  the 
engine  by  adding  first  nitrate  or  acetate  of  lead  and  when  this  is 
thoroughly  mixed  following  with  a  solution  of  potassium  or 
sodium  bichromate.  This  determines  the  precipitation  of  lead 
chromate  upon  the  fibre,  in  a  very  finely  divided  state.  The 
color  produced  is  influenced  by  alkalis,  very  small  amounts  of 
which  are  sufficient  to  darken  the  shade.  Heat  also  influences 
the  shade  to  a  marked  extent  which  necessitates  very  careful 
handling  of  the  paper  on  the  driers  if  irregular  results  are  to  be 
avoided.  As  the  lead  salts  used  are  readily  soluble  in  cold  water 
no  heating  is  necessary  at  this  point  and  for  the  purest  yellows 
the  size  and  alum  solutions  should  also  be  cold  when  used.  The 
choice  between  the  ready  made  paste  color  and  that  prepared  in 
the  beaters  is  largely  a  question  of  personal  preference.  The 
paste  colors  are  comparatively  simple  to  use  and  the  matching  of 
shades  is  much  facilitated  when  they  are  employed;  on  the  other 
hand  the  production  of  the  color  in  the  beater  aids  in  the  fixing 
of  the  color  and  in  the  obtaining  of  even  shades. 
f  Chrome  yellow  is  very  fast  to  light  but  is  destroyed  by  hydro- 
chloric acicD  As  the  lead  salts  are  dangerous  poisons,  their  use 
is  not  to  be  recommended,  and  whenever  possible  the  substitution 
of  yellow  dyes  would  appear  to  be  good  policy. 
£  Chrome  yellow  may  be  converted  into  chrome  orange,  or  basic 
lead  chromate,  by  treatment  with  caustic  soda  or  hot  milk  of 
lime.  This  color  can  be  used  for  unsized  papers  only  as  it  reverts 
to  chrome  yellow  in  the  presence  of  aluminum  sulphate. 
\  Prussian  blue  is  classed  with  the  mineral  colors  because  of  its 
iron  con  tent  A  It  may  be  produced  directly  in  the  beater  by  add- 


PIGMENTS  311 

ing  ferrous  sulphate  followed  by  potassium  ferrocyanide;  the 
white  precipitate  which  is  first  formed  is  rapidly  oxidized  by 
exposure  to  air  with  the  formation  of  the  blue  color.  This  action 
may  also  be  hastened  by  the  addition  of  bleaching  powder  or 
acid  to  the  beater.  As  the  ferrocyanide  is  the  more  expensive  of 
the  two  ingredients  any  excess  is  carefully  avoided  and  it  is 
customary  to  use  three  parts  of  ferrous  sulphate  to  two  of  the 
ferrocyanide  although  two  parts  of  the  sulphate  are  usually 
sufficient  for  the  full  development  of  the  color.  Prussian  blue 
which  has  been  oxidized  in  the  beater  sometimes  causes  the  paper 
to  turn  red  after  some  time.  This  can  be  avoided  by  washing 
the  stock  nearly  free  from  acid  or  better  by  employing  a  Prussian 
blue  prepared  outside  the  beater  and  washed  before  use. 

Paper  colored  with  Prussian  blue  has  the  peculiarity  that 
exposure  to  sunlight  partially  decolorizes  it;  the  full  blue  shade 
is,  however,  again  developed  when  the  paper  is  kept  in  the,  dark 
in  contact  with  the  oxygen  of  the  airj  Prussian  blue  is  affected 
by  alkalis,  particularly  caustic  soda,  which  destroys  the  color 
with  the  formation  of  ferric  hydrate;  treatment  with  acid 
restores  the  color.  When  using  it  in  the  beater  it  is  well  to  see 
that  it  is  added  while  the  reaction  is  slightly  acid  due  to  the 
presence  of  alum. 

Soluble  Prussian  blue  is  produced  when  a  ferric  salt  is  added 
to  an  excess  of  a  solution  of  ferrocyanide.  The  soluble  product 
also  results  if  Prussian  blue  is  boiled  in  a  ferrocyanide  solution. 
It  is  soluble  in  water  but  is  precipitated  by  salts. 

Ultramarines  are  formed  when  aluminum  silicate  is  calcined 
with  sodium  sulphide.  I  In  actual  practice  the  sulphide  is  formed 
from  the  action  of  sulphur  and  carbon  upon  sodium  sulphate  or 
carbonate. 

Ultramarines  are  manufactured  in  various  shades  of  blue  from 
a  greenish  to  a  reddish  tone  and  there  are  even  pure  greens 
which,  however,  find  little  use  in  coloring  paper.  They  are  made 
by  heating  mixtures  of  pure  clay,  sodium  sulphate,  sodium  car- 
bonate, sulphur,  silica  and  charcoal;  the  mixture  after  heating  is 
finely  ground  and  washed.  The  proportions  of  the  ingredients 


312  COLORING 

vary  with  the  different  manufacturers  but  in  general  three  grades 
are  made  as  follows: 

i .  Sulphate  ultramarines  are  those  made  with  sodium  sulphate. 
They  are  the  palest,  are  greenish  in  tint  and  are  most  easily 
attacked  by  alum. 

'  2.   Soda  ultramarines  low  in  sulphur  are  pure  blue  and  darker 
than  the  sulphate  ultramarines. 

•^3.  Soda  ultramarines  high  in  sulphur  and  silica  are  the  darkest 
and  have  a  reddish  tinge.  They  are  the  most  resistant  to 
alum. 

The  finished  ultramarine  contains  sodium,  aluminum,  silicon, 
sulphur  and  oxygen;  its  actual  constitution  is  not  known  and  no 
theory  so  far  proposed  accounts  for  all  its  properties.  UJltra- 
marines  are  absolutely  fast  to  light  and  are  not  changed  by  expo- 
sure to  the  atmosphere  or  by  weak  alkalis.^/  They  are  decom- 
posed by  mineral  acids  with  evolution  of  hydrogen  sulphide  and 
destruction  of  the  color.  They  are  darkened  by  moisture  which 
is  taken  advantage  of  by  unscrupulous  dealers  who  add  water, 
glycerine  or  molasses  to  make  them  appear  of  greater  strength. 
For  this  reason  ultramarine  should  not  be  purchased  on  the  basis 
of  its  appearance  but  actual  coloring  tests  should  be  made.  The 
different  products  vary  in  the  fineness  of  their  particles  and  the 
ease  with  which  they  mix  with  water.  Both  of  these  points 
should  be  considered  since  if  they  are  not  satisfactory  spots  or 
color  streaks  are  likely  to  appear  in  the  paper. 

When  used  for  tinting  in  the  production  of  white  papers  ultra- 
marines give  bright  effects  which  are  hard  to  equal  with  other 
coloring  materials.  If  they  are  used  for  deeper  colors  the  two 
sides  of  the  sheet  are  apt  to  vary  in  shade  because  of  the  loss  of 
pigment  in  passing  over  the  suction  boxes. 
lv Another  pigment  which  is  still  used  occasionally  for  gray  or 
black  papers  is  lamp  black [J  If  used  in  large  proportions  it  tends 
to  cause  streaks  and  specks  in  the  paper  and  to  make  it  smut 
badly.  Its  low  specific  gravity  makes  it  difficult  to  handle  with- 
out getting  it  all  over  the  beater  room  and  uniform  results  are 
hard  to  obtain  because  the  shade  depends  so  much  on  the  length 


ARTIFICIAL  ORGANIC   COLORS  313 

and  nature  of  the  beating  which  the  stock  has  had.  Lamp  black 
is  being  replaced  by  various  mixtures  of  soluble  dyes. 
,  Natural  Organic  Colors.  Colors  of  this  class,  of  a  vegetable 
or  animal  origin,  were  formerly  much  used  in  coloring  paper  but 
they  are  no  longer  employed  to  any  extent  because  of  the  better 
and  cheaper  results  obtained  with  the  coal  tar  colors.  J  For  this 
reason  brief  mention  of  their  names  and  properties  is  all  that 
seems  desirable. 

Annatto  is  derived  from  the  fruit  of  the  annatto  tree  and 

gives  shades  of  orange.     It  is  costly  and  fugitive. 
Turmeric  is  prepared  from  the  roots  of  Curcuma  tinctoria. 

It  dyes  paper  pulp  a  direct  yellow  which  is  fast  to  acids 

but  is  sensitive  to  light  and  alkalis. 

Weld  is  obtained  from  the  blossoms  of  Reseda  luteola.     It 
f          gives  various  shades  of  yellow  according  to  the  mordant 

used.  < 

Quercitron  is  the  powdered  bark  of  Quercus  tinctoria.     It 

gives  yellow  shades  when  used  in  the  same  manner  as  weld. 
Safflower  is  obtained  from  the  petals  of  Carthamus  tinctoria. 

It  gives  pinks  of  great  beauty  but  they  are  fugitive  to  light 

and  air. 
Redwoods.     Various  species  of  Caesalpinia  have  been  used 

for  the  dyeing  of  pink  and  reddish  shades  which  are  not 

very  fast  to  light. 
Cochineal  is  obtained  from  the  cochineal  insect  and  was 

formerly  used  as  a  pink  for  toning  white  papers. 
Cutch  or  Catechu  is  the  dyestuff  obtained  from  Mimosa 

catechu.     It  gives  shades  of  brown  which  are  fast  to  light, 

acids  and  alkalis. 
Logwood  is  obtained  by  extracting  Haematoxylon  campe- 

chianum.     It  is  used  for  blacks  in  conjunction  with  iron 

salts  and  tannic  mordants. 

I  Artificial  Organic  Colors.  This  class  includes  all  the  so-called 
coal  tar  colors  or  aniline  dyes.  They  are  superior  to  other  color- 
ing matters  in  brilliancy  and  purity  of  shade,  coloring  power, 


314  COLORING 

solubility  and  ease  of  application  and  their  chief  drawback  is  lack 
of  fastness  to  light. 

In  using  these  dyes  the  method  of  working  depends  on^the 
fibre  to  be  dyed  and  the  nature  of  the  coloring  matter  usedy  A 
knowledge  of  the  methods  employed  in  textile  dyeing  is  of  con- 
siderable assistance  though  the  impossibility  of  thorough  washing 
in  the  beater  renders  impractical  the  use  of  many  of  these 
methods.  Moreover  since  vegetable  fibres  only  are  used  in 
paper  making  any  methods  which  are  applied  to  wool  or  silk  are  j 
only  of  abstract  interest  to  the  dyer  of  paper.  It  must  be  borne 
in  mind  that  the  different  fibres  in  mixed  stock  may  have  different 
affinities  for  the  coloring  matter  and  by  taking  it  up  in  different 
degree  cause  an  uneven  or  variegated  appearance.  (Jlf  clear  light 
shades  are  desired  only  bleached  pulp  may  be  used  while  the 
heavy,  deep  colors  can  with  advantage  be  obtained  on  unbleached 
stock. 

^Fillers  which  take  up  the  dyes  assist  in  obtaining  even  shades 
and  whenever  possible  the  filler  should  be  selected  with  this  object 
in  view.  To  allow  the  filler  to  absorb  the  greatest  amount  of 
color  it  should  be  added  after  the  dye  but  before  the  size. 

The  combination  of  the  filler  and  the  dyestuff  is  regarded  by 
some  as  a  chemical  phenomenon  while  others  consider  it  purely  a 
physical  action  depending  on  the  ability  of  the  filler  to  form 
colloidal  solutions".  (The  amount  of  dye  taken  up  by  different 
fillers  has  been  determined  by  Heuser  l  who  gives  in  the  following 
table  the  percentage  of  the  added  dyestuff  taken  up  by  the  filler 
when  10  grams  of  the  latter  are -treated  with  0.4  gram  of  color. 

1  E.  Heuser:  Wochbl.  Papierfabr.,  1914,  2288  and  2470. 


ARTIFICIAL  ORGANIC   COLORS 


315 


i 

2 

3 

4 

5 

6 

Color 

Asbes- 
tine 

Blanc 
fixe 

Bohemian 
earth 

China 
clay 

Kaolin 

Talc 

Malachite  green  
Crystal  violet  
Manchester  brown  
Safranine  
Chrysoidine  

96.65 
99-97 
97.83 
84.82 
96.10 

32.40 
25.96 
28.25 
33-iQ 
25.82 

28.62 
62.93 
40.00 
53.48 
62.35 

45-32 
56.91 
40.87 

66.45 
41  .87 

72.75 
64.68 
72.86 
41  .12 

CC    Ql 

49-95 
60.56 
40.62 
30.06 

3C  .  C2 

Alkali  blue 

66  10 

1C    C2 

48  ac 

•21      Jf 

2  C.     73 

3  £.     26 

Acid  magenta 

60  81 

18  70 

4-O     O7 

4-^    2Q 

^•/J 

2O    OO 

4Q   80 

Ponceau 

18   42 

23    IO 

31  80 

44    1C 

22     CO 

CA   27 

Cotton  scarlet  . 

68  75 

•2-2    47 

41  oo 

4C,    62 

2O    2C 

60   12 

Napthol  yellow  

Diamine  green  
Dianil  blue  

25.00 

58-50 
06.32 

5-75 
19.61 

7O  .41? 

5-oo 
32-58 

48  ,O3 

16.52 

37-92 
38.0Q 

0.52 

35-45 

C,3    03 

'  25.45 

5O.OO 
60.76 

Diamine  violet  
Diamine  heliotrope  
Diamine  purpurine  

68.48 
60.59 
59  .89 

31.84 
3LI7 
5O.O2 

29-53 
46.25 

47  -51 

35-57 
39-71 
56  .  14 

52-95 
30.24 
43  .03 

69.11 
65.85 
60.48 

The  following  figures  by  H.  Strom  1  show  the  color  absorbed  in 
grams  by  i  gram  of  filler  from  100  c.c.  of  o.i  per  cent  solution  of 
the  dyestuff. 


Asbestine 

Blanc  fixe 

Talcum 

Kaolin 

China  clay 

Malachite  green  .  . 

O  005786 

o  00371=; 

O    OOsOCS 

o  00842^ 

o  008425 

Safranine,  cone  .  . 

o  007752 

o  004877 

o  007  7  c.  2 

O   OOQQ4I 

O  OOQQ4I 

Paper  Scarlet  ex  
Dianil  yellow  R  
Dianil  red  R  
Eosine  ex.  5  B. 

0.003715 
0.005786 
0.008039 
o  000900 

0.002251 
0.006712 

0  .010000 

o  oo  2  7  64 

0.003237 

0.004518 
0.006526 
o  002764 

0.001914 
0.005603 
0.006526 
o  002036 

0.003237 
0.004518 
o  .  009404 

O    OO2CQ3 

Paper  deep  black,  cone.  . 

0.005970 

0.007277 

0.004877 

0.003633 

0.006712 

Not  all  dyes  of  the  same  class  are  taken  up  to  the  same  extent 
by  the  same  filler.  Acid  dyes  can  be  removed  almost  com- 
pletely from  fillers  by  washing  with  hot  or  cold  water;  basic  colors 
fix  themselves  on  silicates  but  even  basic  colors  can  be  washed 
out  of  blanc  fixe. 

Apart  from  all  questions  of  the  theory  of  dyeing  the  coloring 


1  Strom:  Wochbl.  Papierfabr.,  44,  4516. 


316  COLORING 

of  paper  pulp  is  not  only  a  question  of  forming  and  fixing  colored 
precipitates  where  pigments  are  concerned  but  also  of  fixing  the 
soluble  colors  firmly  on  the  fibres  by  means  of  mordants.  Coal 
tar  colors  which  form  no  precipitates  with  metallic  salts  and 
which  are  not  fixed  on  the  fibres  when  the  pulp  is  acidified  are  of 
no  use  in  coloring  paper.  The  mordants  in  some  cases  serve  to 
fix  the  color  upon  the  fibre  and  make  it  more  fast  to  washing, 
light,  etc.,  while  in  other  cases  they  combine  with  the  dye  as  an 
essential  constituent  without  which  it  would  be  uncolored  or  a 
worthless  shade.  Mordants  are  of  two  general  classes,  acid 
mordants,  such  as  tannic  acid  and  the  fatty  acid  compounds  used 
for  fixing  basic  dyes;  and  basic  mordants,  consisting  of  the 
hydrated  oxides  of  the  heavy  metals  as  tin,  copper,  chromium, 
iron,  aluminum,  etc.,  which  serve  for  fixing  the  acid  dyes.  Basic 
mordants  are  employed  in  the  form  of  soluble  salts,  such  as  the 
sulphate  or  acetate  of  aluminum,  which  react  with  the  fibre  with 
the  deposition  of  the  base  which  then  attracts  and  fixes  the  color. 
Time  is  required  for  this  reaction  and  different  mordants  give 
different  colors  with  the  same  dye.  /Cotton  has  little  affinity  for 
ordinary  metallic  salts  but  if  they  are^present  in  very  basic  con- 
dition it  may  decompose  them  with  the  loose  fixation  of  metallic 
hydroxides.  Tannin  on  the  other  hand  has  a  direct  affinity  for 
cotton  and  may  be  still  more  firmly  fixed  by  the  use  of  tartar 
emetic  or  glue.  Linen  is  similar  to  cotton  but  is  even  more 
difficult  to  dye.  While  not  strictly  a  mordant  rosin  size  gives  to 
fibres  some  of  the  properties  of  animal  fibres  and  enables  ttiem 
to  take  up  many  colors  without  the  use  of  any  other  mordant] 
The  use  of  mordants,  other  than  rosin  sizing,  is  not  nearly  so 
general  in  the  paper  industry  as  in  textile  work  and  in  many 
mills  they  are  never  employed. 

[The  water  used  in  dyeing  operations  may  have  a  considerable 
influence  on  the  results.  Finely  divided  vegetable  impurities 
have  little  effect  on  either  colors  or  mordants  but  inorganic  im- 
purities are  much  more  serious^;  Hard  water  due  to  carbonates  or 
bicarbonates  of  calcium  or  magnesium  may  cause  partial  pre- 
cipitation of  basic  colors^  if  it  is  necessary  to  use  such  water  for 


DIRECT   COTTON   COLORS  317 

dissolving  basic  colors  it  should  be  corrected  by  adding  a  very 
slight  excess  of  acid,  preferably  acetic  acid.  Salts  of  iron  in  the 
water  are  particularly  bad  as  they  discolor  the  fibres  and  act 
as  mordants  with  the  production  of  bad  shades. 

Dyes  should  not  be  added  to  the  beater  in  the  dry  state  except 
in  very  special  cases,  as  sooner  or  later  trouble  with  color  specks 
will  be  encountered.  They  should  be  dissolved  in  soft,  or  con- 
densed, water  and  strained  through  a  hair  sieve  or  through  wet 
flannel  before  being  used.  The  amount  of  water  necessary  varies 
greatly  but  in  general  is  more  for  basic  than  for  acid  dyes;  with 
some  of  the  former  it  may  be  necessary  to  use  as  much  a,s  200 
Ibs.  of  water  for  i  Ib.  of  color.  Most  colors  may  be  heated  nearly 
to  boiling  without  danger,  but  a  few,  as  auramine,  methyl  green, 
etc.,  are  injured  by  boiling  and  should  not  be  heated  above 
1 60°  to  170°  F.  If  the  color  separates  from  solutions  which  have 
been  made  some  time  it  may  be  redissolved  by  heating  and 
stirring.  Some  colors  are  insoluble  or  slightly  soluble  in  water 
and  in  this  case  equal  parts  of  methyl  alcohol  and  water  may  be 
used. 

^fhe  dyestuffs  are  variously  classified  by  different  writers. 
Direct  or  substantive  colors  are  those  which  color  the  fibres 
directly  without  the  use  of  a  mordant;  they  are  fully  developed 
colors  and  always  give  the  same  shade,  either  weaker  or  stronger 
according  to  the  amount  used.  Mordant  or  adjective  colors  are 
those  which  must  be  treated  by  chemical  means  in  order  to 
develop  the  true  colors.  This  group  forms  with  metallic  oxides 
insoluble  precipitates  or  lakes  on  the  fibre.  Colors  which  are  of 
interest  to  the  paper  maker  may  be  divided  into  four  principal 
groups  as  follows:  (i)  direct  colors,  (2)  basic  colors,  (3)  eosines 
and  rhodamines  and  (4)  acid  colors.  The  grouping  of  the  acid 
colors  separately  is  for  practical  rather  than  scientific  reasons 
since  the  dividing  line  between  the  acid  and  the  direct  cotton 
colors  is  not  at  all  sharp,  jl 

[^Direct  Cotton  Colors.  These  may  be  used  on  unmordanted 
fibres  in  a  neutral  or  alkaline  condition  and  they  can  be  used 
mixed  with  each  other  in  the  same  bath.  Acid  colors  may  usually 


318  COLORING 

be  mixed  with  the  direct  colors  and  used  together  though  basic 
colors  should  never  be  mixed  with  direct  colors  either  dry  or  dis- 
solved. Dyeing  with  the  direct  colors  is  best  done  at  the  boiling 
temperature  though  it  may  also  be  done  warm  or  even  cold.  If 
the  stock  is  not  heated  the  backwater  is  apt  to  be  colored.  Salt  to 
the  extent  of  75  Ibs.  to  a  i,ooo-lb,.  beater  is  also  desirable  to  assist 
the  fibre  in  taking  up  the  dye.,/  Under  most  conditions  the 
colors  tend  to  bleed  from  the  fibres  when  they  are  mixed  with 
white  fibres  so  that  they  are  not  satisfactory  for  granite  papers. 
This  can  be  prevented  to  a  certain  extent  by  topping  with  basic 
colors  and  it  is  also  claimed  that  by  adding  10  Ibs.  of  Glauber 
salt  per  100  Ibs.  of  fibre  and  boiling  for  three  quarters  of  an  hour 
fastness  to  water  can  be  insured.  The  direct  cotton  colors  are 
usually  precipitated  by  lime  and  magnesia  and  water  containing 
these  substances  should  be  corrected  by  boiling  with  soda 
ash. 

These  colors  are  particularly  desirable  for  blotting  papers  and 
tissues  where  sizing  cannot  be  used;  they  are  also  equally  ser- 
viceable for  sized  papers,  j  They  exhaust  well  and  a  colorless 
backwater  is  usually  obtained.  They  vary  greatly  in  fastness  to 
light,  some  being  fully  as  fugitive  as  the  basic  colors  while  others 
are  among  the  fastest  colors  known.  Certain  of  the  direct  blues 
are  increased  in  light  resistance  by  adding  a  little  copper  sulphate 
to  the  beater  after  the  dye  has  been  taken  up  by  the  fibre.  When 
i  per  cent  or  less  of  the  dyestuff  has  been  used  2  per  cent  of  cop- 
per sulphate  should  be  added  but  if  over  i  per  cent  of  dye  has  been 
employed  an  equal  weight  of  the  sulphate  will  be  sufficient. 

Basic  Colors  are  salts  of  organic  bases  of  artificial  origin,  the 
base  containing  the  color  bearing  group.  Most  commercial 
basic  colors  are  hydrochlorides,  though  sulphates,  acetates,  oxa- 
lates,  nitrates  or  even  double  salts  of  hydrochloric  acid  and  zinc 
chloride  are*  also  met  with.  !ln  rare  cases  the  color  base  is  used. 
All  basic  colors  are  decolorized  by  reducing  agents  as  zinc  and 
hydrochloric  acid.  Some  are  decomposed  into  other  substances 
so  that  the  color  cannot  be  regenerated  but  with  most  a  colorless 
or  "leuco  compound"  is  formed  which  is  easily  oxidized  to  the 


EOSINES  AND   RHOD AMINES  319 

niginal  color.  In  dyeing  with  basic  colors  the  salts  decompose, 
he  basic  part  combining  with  the  acid  present  in  the  fibre  or 
Lxed  thereon  by  mordanting  with  tannic  acid.  The  nature  of  the 
aordant  or  of  the  fixing  metal  does  not  greatly  affect  the  shade 
>f  any  given  dye. 

JBasic  colors  have  very  great  tinctorial  power  and  are  generally 
>f  pure  and  brilliant  shades.  They  are  fugitive  to  light  but 
>ecause  of  their  great  coloring  power  they  are  extensively  used 
yhere  permanence  is  not  of  the  utmost  importance^'  The 
.ffinity  of  all  fibres  for  basic  dyes  is  not  the  same^o  when  mixtures 
ire  being  treated  uneven  dyeing  may  result;  this  can  be  avoided 
o  a  great  extent  by  adding  a  little  alum  before  the  color  or  by 
,dding  the  dye  in  a  very  dilute  condition.  ^When  the  fibres  have 
u  considerable  affinity  for  the  color,  as  with  sulphite  and  jute, 
he  dyeing  may  be  done  with  the  aid  of  rosin  and  alum  or  even 
!um  only  but  for  absolute  fastness,  as  for  use  in  making  granite 
>apers,  mordanting  with  tannin  is  necessary.  With  unbleached 
ulphite  there  is  a  very  strong  tendency  to  absorb  the  color  and 
o  avoid  uneven  dyeing  it  is  well  to  use  the  color  in  very  dilute 
olution.  For  ground  wood  pulp  basic  colors  are  especially 
uitable  and  the  dyeing  should  be  done  hotj 

Basic  colors  may  be  used  mixed  with  each  other  but  never 
nixed  with  either  acid  or  direct  colors  since  precipitation  re- 
ults.  If  it  is  necessary  to  use  both  classes  of  color  they  should 
>e  dissolved  separately  and  added  separately  to  the  beater. 
^Eany  of  the  lakes  formed  by  basic  and  direct  colors  are  decom- 
>osed  at  70°  C.,  or  even  below,  so  where  both  are  used  it  is  well 
o  avoid  high  temperatures.  The  use  of  acid  and  basic  colors 
ogether  gives  colorless  backwater;  to  obtain  the  best  results 
t  is  well  to  use  the  basic  dye  first  and  top  with  the  acid 
:olor.  The  exhaustion  of  the  color  is  also  aided  by  the  filler 
yhich  readily  takes  it  up  at  comparatively  moderate  tempera- 
ures. 

JEosines  and  Rhodamines.  Commercial  eosines  are  alkali 
alts  of  chlorine,  bromine,  iodine  or  nitro-substitution  products 
>f  fluorescein  or  some  of  its  derivatives,  while  rhodamines  are 


320  COLORING 

basic  hydrochlorides  of  organic  basesT]  Rhodamine  B,  for  in- 
stance, possesses  both  acid  and  basic  properties  while  the  cosines 
have  the  properties  of  feeble  acids.  All  of  this  group  form 
leuco  compounds  on  reduction  and  regenerate  more  or  less  rap- 
idly on  oxidation  but  not  always  to  the  same  compound  as  the 
halogen  is  frequently  removed  by  the  reducing  agent. 

The  cosines  are  mostly  soluble  in  soft  water  or  dilute  alcohol, 
but  with  hard  water  insoluble  lakes  are  formed  so  that  such 
water  must  be  corrected  with  soda  ash.  Rhodamines  may  be 
dissolved  as  with  basic  colors.  Solutions  of  the  eosines  show 
more  or  less  fluorescence  particularly  in  alcoholic  solution  or 
in  the  presence  of  ammonia.  Eosines  are  fast  to  alkalis  but 
not  to  mineral  acids;  they  are  also  affected  by  alum  to  a  harm- 
ful extent  so  that  an  excess  of  the  latter  should  be  avoided. 
They  have  very  slight  affinity  for  vegetable  fibres  and  their 
fixation  is  due  largely  to  the  sizing.  They  form  lakes  with 
metallic  salts,  those  with  lead  being  particularly  brilliant;  to 
obtain  the  best  shades,  therefore,  sugar  of  lead  may  be  used  in 
the  beater. 

CEosines  dye  shades  from  yellowish  to  bluish  red;  they  are 
remarkably  brilliant  but  are  very  fugitive.  Rhodamines  are 
also  very  brilliant  and  are  much  faster.  They  are  not  much 
used  on  cotton  because  they  cannot  be  permanently  fixed  on 
the  fibre  without  impairing  their  brilliancy^ 
PAcid  Colors.  Acid  colors  are  of  three  groups  (i)  nitro  com- 
pounds, (2)  azo  compounds  and  (3)  sulphonated  basic  colorsTj 
They  are  decolorized  by  reducing  agents  but  are  differently 
affected;  nitro  compounds  are  converted  into  amino  compounds 
from  which  the  coloring  matter  cannot  be  regenerated;  azo 
compounds  decompose  with  breaking  up  of  the  azo  group  and 
cannot  readily  be  linked  up  again;  while  the  sulphonated  basic 
colors  form  leuco  compounds  from  which  the  color  can  be 
regenerated. 

L_Acid  colors  can  oe  mixed  with  each  other  to  produce  com- 
pound shades.  They  are  riot  suitable  for  unsized  papers  as  they 
have  comparatively  little  affinity  for  fibres  and  cannot  be  fixed 


VARIOUS  APPLICATIONS  321 

on  cotton  or  linen  to  resist  washing.  Rosin  sizing  is  essential 
for  good  results  especially  for  deep  shades  and  better  fixation  is 
obtained  if  the  color  is  added  long  enough  before  the  size  to 
insure  thorough  mixing  before  the  latter  is  added.  As  a  rule 
acid  colors  have  comparatively  little  tinctorial  power.  They 
are  quite  variable  in  fastness  to  light  but  are  generally  more 
fast  than  basic  dyesT^ 

Miscellaneous.  Not  mentioned  in  any  of  the  previous  groups 
are  certain  organic  pigments  especially  the  indanthrenes.  These 
belong  to  a  class  of  vat  dyes  which  in  textile  work  yield  shades 
which  are  remarkably  fast  to  light.  While  a  number  of  vat 
colors  are  used  in  textile  work  the  only  ones  which  have'  been 
tried  for  coloring  paper  are  the^blue  indanthrenes.  ,  These  are 
sold  in  the  form  of  paste  colors,  being  insoluble  in  water  and 
dilute  acids  or  alkalis.  They  are  used  in  the  same  way  the 
pigments  are  and  have  the  common  fault  of  all  paste  colors 
that  the  strength  of  the  color  is  continually  changing  because 
of  the  loss  of  water  through  evaporation.  The  colors  obtained 
with  indanthrene,  at  least  where  tints  are  concerned,  are  not 
particularly  bright  and  as  a  class  they  have  little  to  recom- 
mend them  except  their  great  fastness  to  light. 

Various  Applications.  The  foregoing  ^remarks  apply  chiefly 
to  the  coloring  of  paper  stock  in  the  beater.  The  coloring  of 
coating  to  be  applied  to  the  surface  of  the  paper  follows  similar 
lines,  except  that  the  colors  used  must  in  general  be  fast  to 
alkalis  since  satin  white  contains  considerable  amounts  of  free 
lime  and  the  casein  is  usually  treated  with  an  excess  of  alkali  in 
dissolving.  When  pigments  are  used  in  coating  they  must  be 
very  finely  divided  and  easily  broken  down  into  their  ultimate 
particles  since  lumps  of  color  will  crush  when  calendering  and 
form  spots  or  streaks. 

A  third  method  of  coloring  is  that  known  as  stuffing,  padding, 
or  calender  staining.  Here  the  color  is  applied  to  the  surface 
of  a  web  of  paper  as  it  passes  through  the  calenders.  Soluble 
colors  are  necessary  for  this  work  and  for  absorbent,  or  very 
slightly  sized,  paper  the  solution  may  be  made  with  water.  If 


322  COLORING 

the  paper  is  hard  sized,  the  color  may  be  dissolved  in  denatured 
alcohol  to  make  it  penetrate  the  paper  slightly.  Acid  dyes  are 
much  used  for  this  type  of  work?^ 

£jFor  the  production  of  heavy  colors  a  saving  of  dye  is  some- 
times made  by  coloring  the  stock  partly  in  the  beater  and  when 
the  paper  is  partly  dried  on  the  first  section  of  driers  running 
it  through  a  vat  of  the  color  solution,  then  through  squeeze 
rolls  and  finally  over  the  rest  of  the  driers/"? 

Testing  Colors.  The  tests  which  it  is  desirable  to  apply  to 
colors  are  those  which  will  show  whether  the  material  is  of  the 
same  shade  and  strength  as  the  standard.  In  the  case  of  new 
samples  it  is  necessary  to  compare  their  color  and  tinctorial 
power  with  dyes  already  in  use,  and  also  to  apply  tests  to  show 
whether  they  are  sufficiently  fast  to  the  chemicals  with  which 
they  will  come  in  contact. 

The  most  satisfactory  method  of  testing  colors,  though  by 
no  means  the  quickest,  is  to  color  up  a  weighed  amount  of  stock 
which  has  been  beaten,  sized  and  loaded  in  a  small  beater. 
Sheets  made  from  this  stock  and  dried  will  then  give  a  perma- 
nent record  of  the  shade  and  strength  of  the  color  in  question. 
This  method  can  be  applied  equally  well  to  dyes  and  pigments 
but  it  is  not  very  satisfactory  for  tints,  such  as  the  blue-  or 
pink-whites,  of  the  book  or  writing  paper  class. 

With  soluble  colors  the  following  method  has  proved  satis- 
factory in  most  cases.  Prepare  a  solution  of  one  part  of  the 
dye  in  1000  parts  of  water,  noting  carefully  any  insoluble  resi- 
due. From  this  solution  remove  two  samples  of  50  c.c.  and 
25  c.c.  respectively,  place  them  in  separate  beakers  of  about 
300  c.c.  capacity,  and  dilute  each  to  exactly  250  c.c.  From  a 
stock  supply  of  dry,  bleached,  sulphite  fibre  prepare  strips  of 
the  same  size  which  will  fit  easily  into  the  beakers  of  the  diluted 
dyes.  Plunge  these  strips  into  the  solutions  for  exactly  one 
minute,  remove,  drain  and  air  dry.  They  can  then  be  com- 
pared with  the  standard  strips  for  shade  and  strength.  For 
some  of  the  very  strong  basic  colors  it  is  well  to  use  25  and 
10  c.c.  instead  of  50  and  25.  It  is  obvious  that  this  test  is 


TESTING  COLORS  323 

comparative  only  and  that  the  quantities  and  volumes  may  be 
varied  to  suit  the  wishes  of  the  observer. 

With  pigments  the  following  test  has  proved  very  convenient. 
Weigh  into  a  porcelain  cup  100  grams  of  clay  and  3  grams  of 
the  pigment.  Mix  this  with  70  to  75  c.c.  of  water  and  then 
add  60  grams  of  a  casein  solution  containing  exactly  12  grams 
of  casein.  Mix  the  contents  of  the  cup  very  thoroughly  and 
by  means  of  a  brush  or  some  sort  of  a  scraping  device  apply  a 
very  thick  coat  of  the  mixture  to  small  sheets  of  white  paper. 
When  these  sheets  are  dry,  preferably  air  dried,  they  are  com- 
pared with  the  standard  sheets  for  color.  This  test  also  is 
comparative  only  and  to  make  it  of  value  the  same  clay,  casein 
and  paper  must  be  used  in  every  case. 

Fastness  to  chemicals  may  be  determined  by  treating  a  dilute 
solution  of  the  dye  with  small  quantities  of  the  chemicals  with 
which  it  will  come  in  contact.  By  making  the  tests  with  solu- 
tions of  definite  strength  and  using  the  same  volumes  each  time 
the  effects  of  the  chemicals  on  the  different  dyes  can  be  more 
readily  compared.  It  is  well  to  make  the  test  first  by  noting 
the  effect  of  standing  several  hours  in  the  cold  and  finally  by 
bringing  the  solutions  just  to  a  boil. 

For  use  in  vulcanized  fibre  the  colors  should  be  fast  to  zinc 
chloride  solution.  This  is  best  determined  by  coloring  some  of 
the  stock  with  the  dye  to  be  tested,  passing  the  sheet  through 
a  bath  of  zinc  chloride  of  the  correct  strength,  and  finally 
washing.  This  will  show  whether  the  color  is  affected  and 
also  whether  it  will  bleed  during  the  washing  of  the  finished 
product. 

Fastness  to .  light  may  be  determined  by  exposing  strips  of 
paper,  colored  with  the  dye  to  be  tested,  in  a  printing  frame 
in  such  a  way  that  part  of  the  strip  is  protected  from  the  light. 
If  daylight  is  used  it  is  difficult  to  duplicate  the  test  because 
of  the  variation  in  the  quality  of  the  light  from  day  to  day  and 
at  different  times  of  the  year.  This  can  be  avoided  by  using 
artificial  light  rich  in  the  ultra  violet  rays  which  are  the  ones 
most  active  in  the  fading  of  colors.  Such  apparatus  intensifies 


324  COLORING 

the  fading  effect  and  enables  results  to  be  obtained  in  a  com- 
paratively short  time. 

It  is  very  seldom  that  it  is  necessary  to  determine  what  dye 
was  used  in  coloring  a  given  sample  of  paper,  usually  it  is  suffi- 
cient to  be  able  to  match  the  shade.  The  determination  of 
the  dyestuff  used  is  a  difficult  matter  at  best  and  is  greatly  com- 
plicated when  more  than  one  dye  was  used,  which  is  generally 
the  case  with  colored  papers.  If  it  is  necessary,  the  scheme 
proposed  by  A.  G.  Green  1  for  the  determination  of  dyes  on 
vegetable  fibres  is  probably  the  best  one  to  follow.  The  iden- 
tification of  the  dyes  themselves  may  be  carried  out  according 
to  the  schemes  of  A.  G.  Green2  and  S.  P.  Mulliken.3  The 
general  properties  of  the  different  classes  of  dyes  have  already 
been  described  and  it  is 'usually  sufficient  to  determine  to  what 
class  or  group  the  sample  belongs,  since  this  information  fixes 
the  dye  method  to  be  used. 

It  is  often  desirable  to  know  whether  a  commercial  product 
is  a  simple  dye  or  a  mixture.  If  the  dyes  have  been  mixed  in 
the  powdered  state,  the  fact  that  it  is  a  mixture  may  be  ascer- 
tained by  taking  a  small  sample  on  the  end  of  a  spatula  and 
blowing  it  onto  a  piece  of  wet,  white  blotting  paper.  Each 
speck  of  color  gradually  dissolves  and  the  various  colors  of  a 
mixture  show  very  plainly  and  can  be  tested  by  chemical  means. 
When  the  coloring  matters  have  been  mixed  in  solution  and 
evaporated  together  this  test  fails.  For  such  cases  the  dye  can 
be  tested  by  making  a  succession  of  dyeings  of  wool  or  cotton 
skeins  in  the  same  dye  bath.  If  the  dye  is  a  mixture  the  first 
and  last  skeins  will  differ  in  shade. 

1  Green:  J.  Soc.  Dyers  and  Colorists,  1907,  252. 

2  Green:  J.  Soc.  Chem.  Ind.,  1893,  p.  3. 

3  Mulliken:  Identification  of  Pure  Organic  Compounds,  Vol.  Ill,  Commercial 
Dyestuffs. 


CHAPTER  XII 
COATED   PAPERS 

The  class  of  papers  variously  known  as  coated  or  glazed,  and 
in  England  as  art  papers,  has  been  developed  within  compara- 
tively recent  years  in  response  to  the  demands  of  the  printers 
for  a  paper  on  which  half-tones  could  be  reproduced  to  good 
advantage.  The  essential  feature  of  such  papers  is  a  thin  layer 
of  mineral  matter  and  adhesive  applied  to  the  surface  of  an 
ordinary  sheet  of  paper,  the  function  of  the  mineral  matter 
being  to  form  the  surface  for  printing,  while  the  adhesive  is 
merely  added  to  hold  this  mineral  matter  on  the  paper  and 
prevent  its  being  removed  by  the  ink.  The  coating  covers  the 
individual  fibres  on  the  surface  of  the  paper  and  in  addition  fills 
in  any  hollows  or  irregularities  between  them  so  that  when  the 
paper  is  calendered  there  results  a  fine,  smooth,  even,  and  con- 
tinuous surface  which  permits  the  finest  dots  of  the  half-tone 
screens  to  take  perfectly.  Such  papers  are  used  for  lithographic 
work,  for  magazine  and  other  printing  and  especially  for  the 
higt  class  half-tones  in  catalogues  and  advertising  matter. 

While  coated  papers  possess  advantages  from  the  standpoint 
of  the  printer,  they  also  have  certain  defects  which  are  of  a 
quite  serious  nature.  The  body  stock  is  frequently  made  of 
inferior  materials  while  the  coating,  due  to  its  nitrogenous 
nature,  is  peculiarly  subject  to  decay  and  to  the  attacks  of 
insects,  especially  when  stored  in  warm,  damp  places.  The 
paper  is  also  very  heavy  and  bulky  so  that  books  made  from  it 
are  difficult  to  handle  and,  moreover,  it  has  very  poor  folding 
or  bending  qualities  and  is  therefore  much  more  liable  to  injury 
than  uncoated  papers.  It  is  by  no  means  certain  that  coated 
papers  will  not  deteriorate  within  a  comparatively  short  time 

325 


326  COATED  PAPERS 

to  such  an  extent  that  matter  printed  on  them  will  be  valueless 
and  for  this  reason  they  should  never  be  used  for  documents  of 
permanent  or  historic  value. 

The  paper,  or  body  stock,  to  which  the  coating  is  applied, 
need  not  be  of  the  highest  class  since  it  is  entirely  covered  by 
the  coating,  and  hence  inferior  materials  are  frequently  used  in 
its  manufacture.  In  fact  in  Europe  ground  wood  is  often  one 
of  the  principal  ingredients  though  it  is  a  finer  quality  of  ground 
wood  than  is  generally  made  in  this  country.  A  practical  limit 
is  set  to  the  use  of  low-grade  stock  by  the  fact  that  the  coating 
is  more  or  less  translucent  and  does  not  prevent  dirty  or  shivey 
stock  from  showing  in  the  finished  paper. 

Some  of  the  qualities  demanded  in  paper  for  coating  are 
regular  formation,  softness  and  pliability,  freedom  from  fuzz 
and  cockles,  uniformity  of  finish,  and  medium  sizing.  The 
regular  formation  is  essential  if  uniform  finish  is  desired  in  the 
coated  paper,  and, softness  and  pliability  are  necessary  if  the 
paper  is  to  run  well  on  the  coaters  since  a  hard,  rattly  sheet  will 
not  lie  flat,  tends  to  curl  on  the  edges  and  does  not  take  the 
coating  well.  Each  little  fibre  which  stands  up  from  the  sur- 
face in  a  fuzzy  sheet  seems  to  attract  the  coating  so  that  it 
causes  a  mottled  effect;  this  is  particularly  noticeable  when 
the  coating  is  tinted  since  the  color  seems  to  concentrate  itself 
round  the  base  of  each  fibre.  One  of  the  most  important  qual- 
ities to  be  considered  is  the  sizing  of  the  sheet  since  if  it  is 'too 
hard  sized  the  coating  tends  to  lie  on  the  surface  and  be  streaky, 
while  if  it  is  too  slack  sized  the  adhesive  will  be  absorbed,  per- 
mitting the  coating  to  be  weak  "or  necessitating  the  use  of  an 
abnormally  large  amount  of  adhesive.  Defective  sizing  is  much 
more  serious  when  glue  is  used  than  when  casein  is  employed 
since  the  temperature  of  the  drying  lines  is  generally  high  enough 
to  keep  the  former  liquefied  and  thus  permit  its  absorption. 

The  coating  mixture  is  nearly  always  applied  to  the  paper  by 
machinery,  several  different  types  of  apparatus  being  used.  In 
one  the  mixture  is  transferred  from  a  roller  revolving  in  a  trough 
to  a  felt  or  brush,  and  from  this  to  the  surface  of  the  paper; 


APPLYING  THE   COATING 


327 


in  another  the  paper  passes  under  a  roller  which  is  immersed 
in  a  tank  of  the  coating  mixture  and  the  excess  is  removed  by 
squeeze  rolls.  In  either  case 
the  coating  is  immediately 
smoothed  out  and  brought 
into  good  contact  with  the 
paper  by  means  of  brushes 
working  across  its  surface 
with  a  reciprocating  motion. 
The  first  of  these  brushes  is 
comparatively  coarse,  but  they 
gradually  become  finer  till  the 
last,  which  is  very  fine,  to 
eliminate  the  marks  made  by 
the  first.  The  arrangement 
of  this  coating  machine  is  in- 
dicated in  Fig.  39.  After 
leaving  the  brushes  the  paper 
passes  through  a  drying  gal- 
lery heated  by  steam  coils  or 
a  current  of  hot  air  and  when 
thoroughly  dry  is  reeled  up 
ready  for  calendering.  The 
amount  of  coating  applied  by 
this  process  varies  with  the 
purpose  for  which  the  paper 
is  made  and  may  be  anything 
from  a  wash  coat  up  to  35  per 
cent  of  the  weight  of  the  fin- 
ished paper.  According  to  the 
type  of  coating  machine  used, 
both  sides  may  be  coated  at 
one  operation  with  the  same 
color  or  each  side  may  be 
coated  separately  with  the 
same  or  different  colors. 


328 


COATED  PAPERS 


The  adhesives  used  in  coated  paper  are  chiefly  glue  and 
casein,  though  starch  and  albumen  have  been  used  to  some 
extent  and  many  others  have  been  proposed  from  time  to  time. 
The  amount  used  varies  with  the  different  mineral  matters, 
satin  white  requiring  much  more  than  blanc  fixe,  while  clay 
occupies  an  intermediate  position.  If  too  much  adhesive  is 
used  the  paper  tends  to  curl,  the  color  is  not  so  good  and  the 
coating  is  less  porous  so  that  when  printed  the  ink  is  apt  to 
offset  and  to  crawl  or  mottle  instead  of  lying  flat.  Such  paper 
also  takes  a  lower  finish  on  calendering  than  when  less  adhesive 
is  employed.  From  the  point  of  view  of  the  printer,  as  well  as 
for  reasons  of  economy,  it  is  therefore  desirable  to  use  as  little 
adhesive  as  possible.  On  the  other  hand  if  too  little  is  used, 
the  coating  will  "lift"  or  "pick"  when  printed,  especially  if 
heavy  or  tacky  ink  is  used.  This  imposes  a  minimum  beyond 
which  the  adhesive  cannot  be  reduced,  while  as  a  matter  of  fact 
this  minimum  is  seldom  even  approached  because  the  many 
variable  conditions  render  it  necessary  to  employ  a  large  factor 
of  safety.  In  good  work  it  is  seldom  possible  to  use  less  than 
15  Ibs.  of  dry  casein  to  100  Ibs.  of  dry  clay  and  much  more 
frequently  18  to  20  Ibs.  are  used,  while  with  glue  the  quantity 
employed  is  about  20  to  25  Ibs. 

The  influence  of  the  amount  of  casein  in  the  coating  on  the 
tune  required  for  linseed  oil  to  saturate  the  paper,  which  may 
be  taken  as  a  measure  of  the  rapidity  with  which  ink  will  pene- 
trate, is  well  shown  by  the  following  experimental  data. 


Grams  of  casein 
per  100  grams  clay 

Time  in  seconds  for 
oil  to  saturate 

Grams  of  casein 
per  100  grams  clay 

Time  in  seconds  for  oil 
to  saturate 

10 

IS 
20 

20 

37 

I2<? 

25 
30 

780-1020 
Does  not  penetrate 

The  mineral  matter  employed  in  coating  paper  may  be  clay, 
blanc  fixe,  satin  white,  talc,  or  a  number  of  other  substances 
and  they  may  be  used  singly  or  in  mixtures  of  two  or  more. 


i 


FINISHING   COATED   PAPERS  329 

The  character  of  the  finished  paper  depends  very  largely  upon 
the  mineral  matter  used  and  many  different  effects  can  be 
produced  by  a  careful  blending  of  the  various  substances.  Satin 
white  gives  the  smoothest  coating  and  the  highest  finish  of  any 
of  these  materials,  clay  gives  a  lower  finish,  while  blanc  fixe 
takes  less  polish  than  either,  thus  by  a  proper  selection  nearly 
any  desired  finish  may  be  obtained.  The  qualities  demanded 
in  a  coating  substance  are  good  color,  freedom  from  grit  and 
the  property  of  working  up  to  a  good,  fluid  mixture  when  the 
adhesive  is  added.  For  tinted  or  colored  papers  it  should  also 
be  free  from  all  traces  of  acid  since  this  might  injure  the  shade. 
The  color  demanded  of  a  coating  material  is  in  general  'much 
brighter  than  that  which  a  filler  is  expected  to  possess  and  the 
price  paid  is  correspondingly  higher. 

In  addition  to  the  two  main  ingredients  in  the  coating  mix- 
ture, other  substances  are  frequently  used  in  smaller  amounts 
for  special  purposes.  Soaps  or  waxes,  either  in  solution  or  in 
the  form  of  emulsions,  are  added  with  the  object  of  improving  the 
finish;  antifroth  oils  are  used  to  prevent  excessive  foaming  of 
the  coating  mixture;  glycerine,  or  some  of  its  substitutes,  is 
added  to  give  the  coating  increased  pliability  or  folding  power 
and  salt  is  sometimes  employed  to  reduce  the  curling  tendency 
of  the  paper.  Nearly  every  manufacturer  has  in  use  some  such 
modification  of  the  regular  process  which  he  generally  considers 
a  secret,  though  it  often  proves  to  be  quite  widely  known.  There 
is  thus  opened  a  very  wide  field  for  the  employment  of  chem- 
istry in  the  coating  industry  and  it  is  probably  safe  to  say  that 
it  offers  more  and  harder  problems  than  any  other  department 
of  paper  making. 

The  finish  imparted  to  coated  paper  depends  on  the  way  in 
which  it  is  calendered  as  well  as  upon  the  materials  of  the  coat- 
ing; the  damper  the  paper  the  higher  the  finish.  There  is  a 
limit,  however,  to  the  amount  of  moisture  which  can  be  advan- 
tageously left  in  coated  paper  which  is  to  be  calendered,  since  if 
it  is  too  high  the  paper  tends  to  crush  or  blacken  and  the  color 
is  seriously  injured.  The  amount  of  moisture  which  will  cause 


330  COATED  PAPERS 

this  varies  with  different  papers  and  with  the  pressure  put  on 
the  calenders  so  that  no  invariable  limit  can  be  set.  It  is, 
however,  safe  to  say  that  if  the  paper  contains  much  over  5  to  6 
per  cent  of  moisture,  exceeding  care  will  have  to  be  used  in 
calendering  it.  The  finish  of  paper  may  be  considered  as  com- 
posed of  two  factors,  smoothness  and  shine.  The  former  is 
essential  to  good  printing  while  the  latter  is  not,  and  since  it  is 
highly  inartistic  as  well  as  seriously  injurious  to  eyesight,  it 
would  seem  well  to  avoid  it  as  far  as  possible.  This  is  being 
done  by  producing  dull  finish  or  mat  papers  in  which  the  smooth- 
ness is  imparted  by  a  light  calendering,  which  is  done  in  such  a 
way  that  little  friction  is  employed,  so  that  the  polishing  effect 
is  slight.  Another  method  is  to  give  a  very  thin  wash  coat,  on 
thp  coating  machine,  over  a  paper  which  has  been  thoroughly 
smoothed.  This  produces  a  peculiarly  velvety  surface  which 
takes  half-tone  effects  with  very  beautiful  results  but  possesses 
the  slight  defect  that  it  is  easily  scratched,  a  slight  stroke  with 
the  finger  nail  sufficing  to  cause  a  distinct  mark.  Careful  selec- 
tion of  materials  which  do  not  readily  take  a  high  finish,  such 
as  blanc  fixe,  barytes,  precipitated  chalk,  .etc.,  materially  assists 
in  the  minimizing  of  this  defect  and  also  aids  in  the  production 
of  dull  finish  papers  of  the  first  class.  Although  papers  with  a 
very  high  glossy  finish  are  still  largely  demanded,  yet  these  dull 
finish  papers  are  rapidly  growing  in  favor  and  it  is  anticipated 
that  they  will  become  more  popular  as  they  become  more 
widely  known. 

The  printing  qualities  of  coated  papers  are  largely  influenced 
by  the  kind  of  adhesive  used  as  well  as  by  the  amount.  Glue 
coating  possesses  the  property  of  taking  ink  especially  well  while 
casein  is  slightly  more  difficult  to  handle.  This  difference 
caused  trouble  when  casein  was  first  introduced  and  its  general 
use  was  delayed  because  of  the  prejudice  of  the  printers.  It  is 
often  claimed  that  the  reason  for  this  difference  lay  in  the  acid 
reaction  of  glue  coated  papers  and  the  alkalinity  of  those  coated 
with  casein.  This  explanation  is  probably  erroneous  >since  it 
has  been  found  that  casein  coated  papers,  except  those  contain- 


GLUE  331 

ing  satin  white,  are  normally  acid  to  litmus  in  spite  of  the  fact 
that  an  excess  of  alkali  is  almost  always  used  in  preparing  the 
casein  solution.  Except  with  inks  which  are  exceedingly  sensi- 
tive to  acids  or  alkalis  the  reaction  of  the  papers  is  probably 
of  very  little  importance  since  printers  practically  never  make 
any  difference,  in  regard  to  the  ink  used,  between  ordinary 
coated  papers  and  those  containing  considerable  satin  white 
which  are  strongly  alkaline. 

Glue.  Of  the  adhesives  used  for  coating  paper  glue  was  the 
first,  and  for  a  long  time  practically  the  only  one,  and  although 
it  has  been  largely  superseded  by  casein  it  is  still  used  to  some 
extent.  It  was  formerly  the  custom,  in  many  cases,  for  the 
consumer  to  manufacture  his  own  glue  but  it  is  better  practice 
to  purchase  it  of  some  reliable  dealer  as  the  supply  obtained 
in  this  way  is  likely  to  be  more  uniform.  For  convenience  in 
handling,  the  ground  glue  is  to  be  preferred  to  the  sheet  glue, 
since  it  requires  very  little  time  for  soaking  and  the  solution 
can  be  quickly  prepared.  The  quality  best  suited  for  coated 
paper  work  is  a  good  grade  of  hide  glue  but  it  is  undoubtedly 
true  that  much  -inferior  material  is  used,  either  intentionally 
because  of  the  apparent  saving  in  cost,  or  unintentionally  be- 
cause of  its  substitution  by  unscrupulous  dealers.  Poorly  made 
glue  is  apt  to  give  trouble  by  frothing  and  it  probably  lowers 
the  quality  of  the  paper  in  which  it  is  used  though  from  the 
numerous  variables  entering  into  the  manufacture  it  is  frequently 
impossible  to  locate  the  cause  of  inferiority  with  certainty. 

Glue  for  coating  paper  should  be  of  good  color,  free  from 
objectionable  odor,  of  good  strength,  nearly  neutral  in  reaction 
and  for  some  purposes  free  from  grease.  The  grease  if  present 
in  appreciable  amount  tends  to  make  "  birds'-eyes "  in  the  coat- 
ing and  thus  cause  defective  printing.  Too  much  grease  also 
lowers  the  clay  carrying  power  or  strength  of  the  glue.  If  on 
the  other  hand,  the  glue  is  entirely  free  from  grease,  the  coating 
dusts  on  the  calenders  and  the  paper  will  not  take  a  good  finish. 
This  reason  for  dusting  was  suspected  by  one  manufacturer 
who  made  his  own  grease-free  glue  and  when  a  small  amount 


332  COATED  PAPERS 

of  fat  was  added  to  the  glue  solution  the  trouble  entirely 
disappeared. 

A  rapid  semi-quantitative  test  for  grease  may  be  made  by 
coloring  the  glue  solution  intensely  with  some  aniline  dye  and 
then  brushing  it  lightly  onto  white  paper.  If  grease  is  present, 
spots  or  "  birds'-eyes "  will  form  and  the  number  of  these  is 
roughly  proportional  to  the  amount  of  grease.  This  test  also 
gives  an  indication  of  the  way  the  coating  mixture  will  spread 
under  the  action  of  the  brushes.  The  best  quantitative  method 
for  the  determination  of  fat  is  that  of  Kissling  which  is  carried 
out  by  dissolving  20  grams  of  the  sample  in  150  c.c.  of  water 
containing  10  c.c.  of  hydrochloric  acid  (sp.  gr.  1.20).  This  is 
heated  three  to  four  hours  on  the  steam  bath,  using  a  reflux 
condenser,  and  after  cooling  the  fat  is  extracted  by  means  of 
petroleum  ether,  which  is  then  evaporated  off  and  the  residue 
dried  and  weighed.  Good  grades  of  glue  may  contain  o.i  to 
0.6  per  cent  of  fat,  but  it  is  safer  to  use  those  which  run  nearer 
the  lower  figure. 

The  presence  or  absence  of  acidity  in  glue  is  of  even  more 
importance  than  the  question  of  fat  since  in  many  instances 
the  colors  used  are  affected  by  the  acid  to  such  an  extent  as  to 
cause  serious  variations  in  shade.  The  acidity  of  glue  may  be 
determined  with  fair  accuracy  by  dissolving  i  gram  of  the  sample 
in  500  c.c.  of  water,  adding  a  few  drops  of  phenolphthalein  solu- 

N 

tion  and  titrating  with  -  -   alkali.     This  gives  all   free  acid, 

10 

organic  as  well  as  mineral,  and  since  a  number  of  acids  may  be 
present  it  is  well  to  express  the  total  quantity  as  the  equivalent 
percentage  of  sulphuric  acid.  The  percentage  of  acid  in  glues 
is  quite  variable,  often  running  as  high  as  1.2  per  cent,  but  for 
use  with  delicate  colors  it  should  not  be  over  0.2  to  0.3  per  cent. 
The  strength  of  glue  is  often  considered  to  be  proportional  to 
the  firmness  of  the  jelly  which  it  forms,  but  experience  has 
shown  that  the  amount  of  clay  which  a  sample  will  hold  is  not 
always  in  accord  with  its  jellying  powers.  A  much  more  reliable 
test  for  strength  is  described  under  casein. 


CASEIN  333 

Coated  papers  in  which  glue  is  used  are  generally  slightly 
acid  in  reaction  and  they  possess  certain  qualities  of  surface 
and  porosity  not  present  in  casein-coated  papers.  The  change 
from  glue  to  casein  was  delayed  for  this  reason  since  it  involved 
also  a  change  in  inks  and  the  technic  of  printing,  but  the  lower 
price  of  casein  enabled  it  to  force  its  way  gradually  in  till  now 
it  has  almost  wholly  replaced  glue  in  all  ordinary  grades  of 
coated  papers. 

Casein.  Casein  is  a  nitrogenous  body  which  is  present  in 
milk  to  the  extent  of  about  3  per  cent  by  weight.  It  may  be 
separated  from  milk  either  by  the  action  of  acids  or  rennet,  but 
the  rennet  casein  is  relatively  insoluble  in  alkalis  so  that  it  is 
out  of  the  question  for  coated  paper  work.  Acid  caseins  may 
be  prepared  by  the  action  of  any  of  the  mineral,  or  the  stronger 
organic  acids;  or  the  milk  may  be  allowed  to  curdle  spontane- 
ously from  the  formation  of  lactic  acid.  This  latter  procedure 
gives  the  so-called  "  self-soured "  casein,  while  if  acid  has  been 
used  its  name  is  usually  attached  to  denote  the  method  of 
preparation,  as  muriatic  casein,  sulphuric  casein,  etc.  In  this 
country  acid  is  generally  added  to  the  skim  milk,  in  South 
America  much  is  made  by  self-souring,  while  in  Europe  both 
processes  are  used. 

Commercial  casein  is  prepared  from  milk  which  has  been 
freed  as  much  as  possible  from  fat  by  means  of  cream  separa- 
tors. This  skimmed  milk  is  warmed  to  49°  to  50°  C.,  the  acid 
is  added  and  when  the  curd  has  settled  the  whey  is  drawn  off. 
The  curd  is  then  washed  by  hot  water,  drained  on  racks  or 
boards,  shredded,  spread  on  wire  bottom  trays  and  dried  in  a 
current  of  warm  air.  The  dried  curd  is  then  ground  to  any 
desired  degree  of  fineness.  If  a  high  grade  product  is  to  be 
made  great  care  must  be  taken  that  the  wet  curd  is  not  kept 
so  long  that  it  has  a  chance  to  decompose  or  mould  and  the 
drying  temperature  must  be  closely  regulated,  since  if  it  goes 
too  high  the  casein  becomes  orange-brown  and  difficultly  soluble. 
The  kind  of  acid  used  also  exerts  a  considerable  influence  on  the 
character  of  the  product;  that  made  with  muriatic  acid  gives 


334 


COATED  PAPERS 


thick  solutions  which  tend  to  foam  and  to  become  jelly-like  on 
cooling,  the  self-soured  produces  thinner  solutions  which,  on 
cooling,  retain  their  fluidity  to  a  notable  extent,  while  that  made 
by  means  of  sulphuric  acid  occupies  an  intermediate  position. 
The  green  curd  from  any  of  these  methods  can  be  used  to  good 
advantage  in  preparing  the  solutions  for  coating,  but  owing  to 
its  poor  keeping  qualities  it  is  only  obtainable  locally. 

The  nitrogen  in  pure  casein  has  been  found  by  various  in- 
vestigators to  range  from  15.12  to  15.74  per  cent,  hence  the  per- 
centage of  nitrogen  found  in  any  sample  multiplied  by  the  aver- 
age factor  of  6.48  will  give  the  percentage  of  ash-,  fat-,  and 
moisture-free  casein.  Commercial  caseins  have  been  found  to 
contain  about  13  per  cent  of  nitrogen  on  an  average  so  that  the 
factor  to  convert  percentage  of  nitrogen  into  commercial  casein 
would  be  X  7.69. 

The  results  of  examinations  of  samples  of  casein  from  both 
German  and  American  markets  are  given  below  and  show  the 
variations  to  be  expected  in  good  commercial  material.  The 
German  samples  were  tested  by  Hopfner  and  Burmeister,1  while 
the  American  samples  were  analyzed  in  the  author's  laboratory. 


. 

German 

America) 

i 

Max. 

Min. 

Avg. 

Max. 

Min. 

Avg. 

Per  cent 

Moisture.  .  . 

10  t;o 

7.27 

Q.23 

12  .  "? 

x  .4 

Q  .6"C 

Fat                      .               

2.06 

O.  23 

0.8s 

Q.Q 

trace 

3.68 

Ash  
Nitrogen  on  total  sample  

4-95 

17  .  CC 

3-53 
12.52 

4.07 

12  .99 

4-5 

I.O 

3-29 

NaOH  to  neutralize  to  litmus 

3  83 

i  30 

2  .  t;i 

* 

The  specific  gravity  of  commercial  casein  as  received  ranges 
from  1.31  to  1.34  and  the  weight  per  cubic  foot  is  38.6  Ibs.  if 
run  loosely  into  the  container  or  47.8  if  tamped. 

The  moisture  in  casein  has  been  found  to  vary  with  the 
humidity  of  the  surrounding  atmosphere  as  is  shown  by  the 
results  of  tests  on  two  standard  commercial  samples. 

1  Chem.  Ztg.,  36,  1912,  1053. 


CASEIN 


335 


Per  cent  humidity 

Moisture  in 

Sample  I 

Sample  2 

40.6 
47-5 

7.27 
8.27 

7.20 
8.06 

52.7 
62.2 

9-13 

iQ-53 

8.99 
iQ-53 

This  explains  why  a  sample  of  casein  containing  12  to  14 
per  cent  of  moisture  when  received  will,  if  spread  out  in  a  thin 
layer,  lose  weight  very  rapidly  at  first  until  the  moisture  is 
reduced  to  7  to  8  per  cent  and  then  will  gain  or  lose  in  weight 
according  to  atmospheric  conditions. 

Soluble  caseins  which  were  formerly  on  the  market  in  large 
quantities,  and  are  still  met  with  occasionally,  are  merely  mix- 
tures of  ground  casein  and  some  alkali  as  borax,  soda  ash,  etc. 
An  analysis  of  a  representative  sample  gave  the  following  results: 

Per  cent 

Moisture 12.2 

Casein  (free  from  fat,  ash,  and  moisture) 67.  i 

Soda  ash,  Na2CO3 8. 6 

Borax,  Na2B4O7,  10  H2O 3.1 

Fat 1.3 

Ash  insoluble  in  water 9.3 

101.  6 

Such  caseins  are  easy  to  handle  but  they  are  likely  to  keep 
poorly  as  the  alkali  may  absorb  water  and  act  destructively  on 
the  casein,  thus  impairing  its  solubility  and  decreasing  its 
strength.  They  also  limit  the  user  to  the  kind  of  alkali  already 
mixed  with  the  casein  and  do  not  permit  its  proper  adjustment 
to  the  work  in  hand.  A  third  point  against  them  is  that  a 
cheap  alkali  is  paid  for  at  the  price  of  casein  so  that  the  user 
can  make  quite  a  saving  by  buying  both  the  alkali  and  the 
casein  separately  and  mixing  them  himself  in  the  proportions 
he  desires. 

Casein  is  essentially  of  an  acid  nature  and  hence  requires 
treatment  with  an  alkali  to  bring  it  into  solution.  It  forms  two 


336  COATED  PAPERS 

series  of  salts,  those  neutral  to  phenolphthalein  being  called 
basic  casemates,  while  those  neutral  to  litmus  are  known  as 
neutral  casemates.  The  casemates  of  sodium,  potassium,  lith- 
ium and  ammonia  are  readily  soluble,  those  of  calcium,  barium 
and  strontium  are  much  less  so  while  those  of  the  heavy  metals 
are  insoluble,  j 

The  alkalis"  which  have  been  proposed  as  solvents  are  am- 
monia and  ammonium  carbonate,  and  hydroxide,  carbonate, 
silicate,  borate,  sulphite,  and  phosphates  of  sodium.  Of  these 
ammonia  and  the  carbonate,  borate  and  phosphates  of  sodium 
are  the  ones  most  frequently  used  while  caustic  soda  is  generally 
avoided  because  of  its  drastic  action  if  used  in  excess.  If  care 
is  used  caustic  soda  is  one  of  the  best  solvents,  being  cheap, 
quick  in  its  action,  and  giving  as  good  solutions  as  the  more 
expensive  solvents.  The  relative  amounts  of  these  alkalis  re- 
quired to  give  a  neutral  solution  vary  with  the  different  caseins 
as  the  following  figures  from  a  large  number  of  tests  made  with 
high-grade  commercial  solvents  will  show 

i  Ib.  borax,  Na2B407  - 10  H20 

=  0.1736  —  0.2330  Ib.  NaOH  average  0.2020 

=  1.062  —  1.159  Ib-  Na3P(V  12  H2O  average  1.130 

=  1.158  —  1.872  Ib.  Na2HP04* 12  H2O  average  1.419 

In  the  case  of  the  phosphates  the  reaction  evidently  ceases 
when  dihydrogen  sodium  phosphate  is  formed  and  this  supposi- 
tion is  confirmed  by  the  fact  that  the  latter  salt  has  no  appre- 
ciable solvent  action  even  when  used  to  the  extent  of  50  per  cent 
of  the  weight  of  the  casein. 

Practical  application  of  these  solvents  brings  out  certain 
marked  differences;  ammonia  is  one  of  the  quickest  solvents 
and  is  especially  useful  in  dissolving  the  last  traces  of  the  casein, 
the  phosphates  give  thinner  solutions  especially  with  muriatic 
caseins,  while  borax  is  a  reliable  general  solvent  for  most  work 
but  cannot  be  used  with  satin  white.  In  any  case  a  consider- 
able excess  is  to  be  avoided  as  it  is  wasteful,  darkens  the  color 
and  with  most  caseins  causes  a  very  marked  thickening  of  the 


CASEIN  337 

solution.  The  full  strength  of  a  casein  is  developed  if  the 
alkali  used  is  sufficient  to  give  a  solution  neutral  to  litmus  and 
while  a  moderate  excess  does  not  cause  loss  of  strength,  this 
does  take  place  if  a  large  excess  is  used,  particularly  if  the  heat- 
ing is  prolonged.  The  amount  of  alkali  required  to  give  a 
neutral  solution  varies  greatly  with  different  caseins;  with  borax 
the  range  may  be  as  great  as  from  7  to  18  per  cent.  A  diffi- 
cultly soluble  casein  may  be  improved  by  soaking  it  in  10  parts 
of  water  acidulated  with  acetic  acid  and  then  washing.  This 
improves  its  solubility  and  reduces  the  amount  of  alkali  re- 
quired. 

In  very  many  caseins  there  is  a  small  amount  of  insoluble 
matter  which  generally  takes  the  form  of  white  flakes  resembling 
skins  or  envelopes  from  which  the  casein  has  been  dissolved. 
In  some  cases  these  will  dissolve  on  the  addition  of  more  alkali, 
but  usually  it  is  impossible  to  eliminate  them  in  this  way.  They 
are  light  but  bulky  so  that  they  appear  to  be  present  in  large 
amount  while  in  reality  the  percentage  is  very  small,  the  worst 
sample  which  has  been  noticed  containing  only  1.64  per  cent  by 
weight.  Under  the  microscope  the  great  majority  of  these  white 
flakes  are  found  to  consist  of  the  hyphae  of  moulds  so  the  old 
theory  that  they  were  particles  of  albumen  precipitated  by 
overheating  of  the  milk  is  untenable.  Additional  proof  of  their 
nature  has  been  obtained  by  moistening  casein  and  allowing  it 
to  mould,  then  drying  and  grinding  it  to  its  original  fineness. 
Four  samples  thus  treated  showed  white  flakes  amounting  to 
15  to  80  times  those  originally  present  and  all  had  the  same 
microscopic  appearance  as  those  present  before  moulding.  These 
flakes  cause  trouble  by  working  up  into  the  brushes  of  the  coat- 
ing machines  and  after  they  have  collected  in  quantity,  dropping 
off  onto  the  paper  thus  making  spots  which  sometimes  stick  to 
the  calender  rolls  and  break  the  paper.  They  also  cause  the 
brushes  to  work  "  dead  "  and  not  spread  the  coating  well.  These 
flakes,  as  well  as  all  other  undissolved  foreign  matter  or  casein, 
can  be  easily  and  completely  removed  by  centrifugal  clarifica- 
tion of  the  casein  solution  and  the  good  portion  of  a  casein 


338  COATED  PAPERS 

which  is  dirty  or  partially  insoluble  can  thus  be  obtained  in  fit 
condition  to  use. 

Solutions  of  casein  are  very  liable  to  become  spoiled,  especially 
in  the  summer  months,  and  such  solutions  cannot  be  used  both 
because  of  their  extremely  bad  odor  and  because  the  strength 
of  the  casein  is  very  largely  destroyed.  Many  substances  have 
been  proposed  as  preservatives  for  casein  solutions,  among  them 
camphor,  essential  oils,  salicylates,  benzoates,  hexamethylene 
tetramine,  etc.,  but  few  of  them  are  worth  the  added  expense. 
The  proper  selection  of  alkalis  has  a  large  influence  on  the  rate 
of  spoiling,  borax  acting  as  a  good  preservative,  while  ammonia, 
phosphates  or  caustic  soda  permit  rapid  spoiling.  Tests  on  the 
same  casein  with  different  solvents  gave  spoiled  solutions  in 
forty-eight  hours  when  ammonia,  caustic  soda,  or  trisodium 
phosphates  were  used  while  if  borax  was  employed  the  solution 
was  good  at  the  end  of  16  days.  Other  experiments  proved 
that  3  to  4  per  cent  of  borax  on  the  weight  of  the  casein  was 
sufficient,  when  mixed  with  other  alkalis,  to  preserve  the  solu- 
tion as  long  as  it  would  ever  be  necessary  under  normal  working 
conditions,  provided  ordinary  care  was  employed  in  keeping 
the  tanks  and  mixers  clean.  For  this  reason  it  is  a  wise  pre- 
caution to  use  a  small  amount  of  borax  in  preparing  casein 
solutions. 

Another  substance  which  acts  as  a  preservative  but  which  is 
used  primarily  as  a  waterproofing  agent  is  formaldehyde.  This 
is  obtained  commercially  as  a  strong  aqueous  solution  of  the  gas 
and  should  always  be  diluted  with  about  ten  times  its  volume 
of  water  before  adding  to  the  coating  mixture.  Over  2  per  cent 
of  the  strong  solution,  based  on  the  weight  of  the  casein,  will 
cause  thickening  while  ij  to  2  per  cent  can  be  added  safely  if  it 
is  well  diluted  and  stirred  in.  This  amount  is  sufficient  to  make 
the  coating  waterproof  or  washable,  while  even  smaller  quanti- 
ties produce  very  noticeable  waterproofing  effects.  When  small 
amounts  of  formaldehyde  are  used  the  waterproofing  is  slight  at 
first  but  gradually  develops  so  that  paper  which  has  been  stored 
several  weeks  will  show  better  results  than  when  first  made. 


TESTING   CASEIN 


339 


Many  other  substances  are  capable  of  rendering  casein  insol- 
uble but  as  most  of  them  cause  curdling  or  thickening  of  the 
casein  solution  they  cannot  be  applied  when  the  coating  is  spread. 
If  casein  coated  paper  is  moistened  with  solutions  of  salts  of  iron, 
lead,  copper,  aluminum,  magnesium,  zinc,  etc.,  the  casein  is 
rendered  insoluble  to  such  an  extent  that  the  paper  may  be 
safely  washed.  The  use  of  any  of  these  materials  means  putting 
the  paper  through  one  more  process  and  as  the  desired  properties 
can  be  more  cheaply  attained  by  formaldehyde  none  of  them  are 
now  employed;  they  do,  however,  possess  possibilities  worthy  of 
future  investigation. 

Under  normal  conditions  of  storage  caseins  are  apt  to  become 
infested  with  worms,  the  larvae  of  either  moths  or  beetles,  and 
the  deterioration  thus  caused  is  very  marked.  Caseins  affected 
in  this  way  require  less  alkali  to  give  neutral  solutions  and  in  some 
cases  may  lose  as  much  as  50  per  cent  of  their  original  strength 
in  one  year.  The  period  of  greatest  deterioration  is  found  to  be 
in  the  summer,  when  the  worms  are  most  active,  while  in  winter 
very  little  change  takes  place.  Obviously  the  best  conditions 
for  lengthy  storage  would  nearly  approach  those  of  cold  storage 
plants. 

The  tests  which  may  be  applied  to  casein  are  of  two  general 
classes,  chemical  analyses  for  certain  constituents  as  moisture, 
ash,  fat,  or  nitrogen  and  empirical  tests  to  show  certain  proper- 
ties as  solubility,  strength,  and  alkali  required. 

Moisture  may  be  determined  by  drying  in  a  thin  layer  at  100° 
to  105°  C.  for  about  two  and  a  half  hours,  cooling,  and  weighing 
in  a  closed  vessel  to  prevent  reabsorption  of  moisture.  All 
caseins  are  not  equally  sensitive  to  heat  but  none  have  been 
found  which,  under  these  conditions,  suffer  decomposition  which 
is  serious  enough  to  cause  any  appreciable  error.  In  fact  most 
caseins  may  safely  be  heated  much  longer  at  this  temperature,  or 
even  as  high  as  115°  C.,  without  vitiating  the  results. 

The  ash  in  casein  may  be  determined  by  burning  2  to  3  grams 
in  a  silica  dish;  platinum  should  not  be  used  because  of  the 
presence  of  phosphates  which  might  be  reduced  and  injure  the 


340  COATED  PAPERS 

platinum.  In  some  cases  the  ash  is  gray  and  infusible  while  in 
others  it  melts  to  a  clear,  glassy  mass.  Rennet  casein  burns  out 
readily  and  gives  a  high  ash,  while  acid  caseins  are  much  harder 
to  ignite  free  from  carbon. 

Fat  may  be  estimated  by  extracting  the  finely  ground  sample 
in  a  Soxhlet  apparatus  with  ether  and  petroleum  ether,  evapora- 
ting the  solvent,  and  drying  and  weighing  the  fat.  A  more 
accurate  and  rapid  method  is  as  follows:  Soak  2  grams  casein  in 
6  c.c.  water  in  a  small  beaker  and  after  about  half  an  hour  add 
with  constant  stirring  9  c.c.  of  concentrated  sulphuric  acid  (sp. 
gr.  1.84).  Pour  the  solution  into  a  Babcock  skim  milk  bottle  and 
wash  out  the  beaker  with  5  c.c.  water  and  5  c.c.  H2SO4.  Fill  to 
the  base  of  the  neck  with  dilute  sulphuric  acid  (4  c.c.  water  and 
5  c.c  cone.  EfcSCX)  and  whirl  in  the  Babcock  centrifugal  five 
minutes.  Fill  with  dilute  acid,  whirl  two  minutes  and  while 
still  hot  read  the  fat  on  the  graduated  neck.  The  reading  mul- 
tiplied by  nine  gives  the  percentage  of  fat  in  the  casein.  The 
secret  of  this  method  is  in  getting  the  concentration  of  the  acid 
just  right  since  if  it  is  too  strong  the  fat  will  char  while  if  it  is 
too  weak  the  casein  will  not  all  be  in  solution  and  a  reading  will 
be  impossible. 

Nitrogen  is  best  determined  by  the  usual  Kjeldahl  method. 
The  factors  for  converting  this  to  casein  have  been  given  above. 

These  chemical  analyses,  while  giving  information  as  to  the 
purity  of  the  sample  in  question,  do  not  show  how  it  will  work  in 
practice,  whether  it  is  completely  soluble,  how  much  alkali  it  will 
require,  whether  the  solution  will  be  thin  or  thick,  or  whether 
the  casein  has  good  adhesive  strength.  For  the  manufacturer 
of  coated  paper  these  points  are  far  more  important  than  the 
chemical  data  and  while  such  tests  are  for  the  most  part  com- 
parative they  are  quite  simple  to  carry  out  and  are  sufficiently 
accurate  for  practical  purposes. 

The  alkali  required,  the  consistency  of  the  solution,  and  its 
completeness  may  be  determined  at  one  operation  as  follows: 
Soak  50  grams  of  the  finely  ground  casein  in  200  c.c.  of  water  in  a 
weighed  No.  3  breaker  for  about  half  an  hour  then  add  a  weighed 


TESTING   CASEIN  341 

amount  of  the  solvent  and  heat  on  the  steam  bath  with  constant 
stirring.  The  amount  of  solvent  should  be  less  than  will  be 
required  to  give  a  neutral  solution  and  the  kind  is  immaterial  so 
long  as  it  is  capable  of  being  accurately  measured ;  borax  and  triso- 
dium  phosphate  are  very  satisfactory  or  a  standard  caustic  soda 
solution  may  be  added  from  a  burette  in  place  of  weighing  the 
dry  solvent.  When  the  alkali  added  has  all  been  used  up  test 
the  solution  by  dipping  in  it  a  moistened  piece  of  blue  litmus 
paper.  If  the  reaction  is  acid  add  more  alkali  and  repeat  the 
heating  on  the  steam  bath.  This  operation  should  be  continued 
until  the  solution  reacts  neutral  to  litmus,  which  will  be  when  it 
turns  red  litmus  slightly  blue  and  blue  litmus  slightly  red.  '  If  at 
this  stage  the  solution  is  not  complete  it  is  well  to  add  more  alkali 
and  see  if  this  excess  will  bring  into  solution  all  of  that  which  is 
insoluble  at  the  neutral  point.  This  test  indicates  the  minimum 
amount  of  alkali  which  can  be  used  with  the  casein  in  question, 
shows  whether  it  is  good  enough  to  use  without  clarifying  the 
solution  and  by  the  consistency  of  the  solution  tells  the  expe- 
rienced man  much  as  to  the  kind  of  alkali  to  use  and  the  manner 
of  running  it  on  his  coaters.  The  test  is  of  such  a  nature  that, 
so  far  as  the  consistency  of  the  solution  and  its  completeness  go, 
it  does  not  lend  itself  readily  to  numerical  expression.  For  this 
reason  the  interpretation  of  the  test  requires  experience  and  this 
cannot  be  imparted  by  words. 

The  strength  of  a  casein  or  the  amount  of  clay  which  a  given 
weight  of  casein  will  hold  on  the  surface  of  the  paper  is  best  deter- 
mined by  a  method  approximating  actual  coating  operations. 
The  apparatus  is  simple;  a  porcelain  cup  (without  a  handle), 
a  brass  plate,  a  steel  scraper  so  shaped  that  a  thin  coating  of  the 
clay  and  casein  may  be  applied  to  a  sheet  of  paper,  a  copper  stirrer 
flattened  and  bent  at  one  end  so  that  the  contents  of  the  cup 
may  be  thoroughly  worked  over,  and  a  set  of  scales  capable  of 
weighing  down  to  o.i  gram.  One  hundred  grams  of  clay,  pre- 
viously dried  at  100°  C.,  are  weighed  out  into  the  cup  and  soaked 
up  with  70  c.c.  water.  The  casein  solution  which  was  prepared 
in  the  solubility  test  is  so  adjusted,  by  evaporating  or  adding 


342  COATED  PAPERS 

water,  that  each  gram  of  dry  casein  is  equivalent  to  5  grams  of 
solution.  The  clay  and  water  are  now  worked  over  with  the 
copper  stirrer,  the  whole  balanced  up  on  the  scales,  30  grams  of 
casein  solution  added  and  the  mass  stirred  until  homogeneous. 
A  sheet  of  paper  is  then  laid  on  the  brass  plate,  a  little  of  this 
coating  mixture  placed  on  one  end  and  a  thin  but  even  coating 
applied  by  means  of  the  scraper.  What  coating  mixture  remains 
on  the  scraper  is  returned  to  the  cup  which  is  again  balanced 
up,  5  grams  more  casein  solution  added  and  another  sheet  spread. 
This  is  repeated  until  the  dry  casein  used  amounts  to  12  grams 
per  100  grams  of  clay.  The  coated  sheets,  which  are  marked  from 
6  to  12,  according  to  the  amount  of  casein,  are  allowed  to  dry 
and  then  by  looking  through  the  sheets  places  of  uniform  thick- 
ness are  selected  and  marked  on  each.  Short  pieces  of  high  grade 
sealing  wax  are  then  melted  on  one  end,  either  in  a  gas  flame  or 
on  the  surface  of  a  steam  heated  box,  and  applied  to  the  marked 
places  with  a  firm  pressure.  They  are  allowed  to  become  thor- 
oughly cold  and  are  then  removed  from  the  paper  by  a  steady 
vertical  pull.  If  enough  casein  is  present  the  surface  of  the  wax 
will  be  covered  with  fibres  to  the  very  edge,  if  too  little  has  been 
used  the  coating  comes  away  from  the  paper  without  pulling  off 
any  fibre,  while  there  is  usually  an  intermediate  case  in  which 
the  center  of  the  wax  shows  fibre  and  the  edges  clay  only;  this 
would  be  considered  just  on  the  line  between  weak  and  strong. 

This  is  an  excellent  comparative  test  but  it  does  not  show  the 
actual  amount  which  can  be  used  practically,  but  for  several 
reasons  indicates  a  higher  strength  than  the  same  casein  shows 
on  a  large  scale.  It  will  be  found-,  however,  that  if  this  test  shows 
one  lot  to  be  weaker  than  another  it  will  be  necessary  to  use  more 
of  the  former  than  the  latter  when  it  is  put  on  the  coaters.  The 
test  is  also  influenced  by  the  kind  of  clay,  thickness  of  coating, 
nature  of  paper,  etc.,  so  that  it  is  necessary  to  use  standard 
materials  in  carrying  it  out.  This  means  that,  while  it  gives  very 
valuable  comparative  results  in  the  hands  of  experienced  persons 
and  under  standard  conditions,  it  is  not  safe  to  compare  results 
obtained  in  different  laboratories. 


STARCH  343 

/' 

Albumen.  Both  blood-  and  egg-albumen  are  similar  in  some 
respects  to  casein  yet  differ  from  it  by  losing  their  solubility 
if  heated  to  about  75°  C.,  while  casein  may  be  treated  with  boiling 
water  and  still  be  soluble  when  the  correct  proportions  of  alkali 
are  used. 

Solutions  of  either  of  these  may  be  prepared  by  stirring  the 
albumen  into  warm  water  to  which  a  little  spirits  of  ammonia 
has  been  added.  The  temperature  should  not  be  over  20°  C.  and 
the  stirring  must  be  frequent  enough  to  prevent  the  albumen 
from  collecting  and  sticking  on  the  bottom  of  the  container. 
Other  substances  are  also  used  as  assistants  in  dissolving  albumen, 
as  borax,  magnesium  sulphate,  etc.  The  strength  of  albumen  is 
very  nearly  equal  to  that  of  casein,  24  to  28  parts  of  albumen 
doing  the  work  of  22  to  24  parts  of  casein. 

Coatings  prepared  with  albumen  are  not  rendered  so  water- 
proof by  formaldehyde  as  are  casein  coatings;  they  may,  however, 
be  made  washable  by  heating,  preferably  in  the  presence  of  steam. 
Mixtures  of  casein  and  albumen  when  treated  in  this  way  give 
washable  coatings  which  are  good  for  chromo  and  leather  papers 
because  of  their  capacity  to  absorb  printing  ink.  While  under 
certain  conditions  albumen  gives  a  higher  finish  to  paper  than 
does  casein  yet  it  is  seldom  used  because  of  its  high  price  and  in 
many  cases  its  disagreeable  odor. 

Starch.  As  an  adhesive  for  coated  paper  work  starch  has 
many  good  points;  it  is  clean,  of  good  color,  without  odor,  non- 
nitrogenous  and  hence  not  liable  to  putrefactive  decomposition, 
has  good  strength  and  is  cheap.  The  different  starches,  such  as 
corn,  wheat,  cassava,  potato,  etc.,  have  quite  distinct  character- 
istics yet  all  are  sufficiently  alike  so  that  they  may  be  discussed 
as  a  class. 

The  simplest  way  to  prepare  an  adhesive  from  starch  is  to  stir 
the  dry  starch  into  8  to  15  times  its  weight  of  water  and  heat 
to  the  boiling  point.  Different  starches  vary  as  to  the  temper- 
ature at  which  they  gelatinize  and  the  thickness  of  the  paste  they 
produce  but  with  reasonable  amounts  of  water  all  are  too  thick 
to  use  on  the  ordinary  coating  machine.  This  difficulty  may  be 


344  COATED  PAPERS 

overcome  by  modifying  the  starch  by  chemical  treatment  so  that 
it  cooks  thinner  while  at  the  same  time  losing  nothing  in  strength 
but  in  many  cases  actually  gaining  in  adhesive  properties.  Such 
modified  starches  may  be  produced  by  treatment  with  acids, 
acid  salts,  oxidizing  agents,  etc.,  under  very  varied  conditions 
and  the  patents  taken  out  along  such  lines  are  almost  innumer- 
able. The  products  of  these  treatments  resemble  the  original 
starches  in  appearance  but  as  stated  give  much  thinner  solutions 
and  also  have,  according  to  their  method  of  preparation,  minor 
differences  which  sometimes  cause  trouble  on  the  coaters. 

A  well  made  modified  starch  for  coated  paper  work  should 
give  a  light  colored,  thin  solution  when  one  part  of  starch  is 
boiled  with  four  parts  of  water.  This  solution  should  not  thicken 
too  much  on  cooling  or  at  least  should  thin  down  to  its  original 
consistency  on  reheating.  While  there  are  many  such  products 
only  a  few  give  satisfactory  mixtures  with  clay  as  most  are  lack- 
ing in  the  property  which  glue  and  casein  possess  of  making  the 
clay  into  a  very  fluid  suspension.  The  lack  of  this  quality 
causes  the  coating  mixture  to  work  "dead"  or  draggy  and  the 
paper  is  apt  to  show  brush  marks,  or  if  these  results  are  to  be 
avoided  so  much  water  has  to  be  added  that  the  drying  lines  are 
overtaxed  and  the  capacity  of  the  machine  is  reduced.  The 
strength  of  starch  has  been  found  to  be  slightly  less  than  that  of 
•casein  so  that  about  20  to  25  Ibs.  are  required  to  do  the  work  of 
1 8  to  20  Ibs.  of  casein. 

Coated  papers  prepared  with  starch  do  not  take  such  a  high, 
glossy  finish  as  casein  coated  papers,  partly  because  of  the  larger 
amount  of  adhesive  used  and  partly  because  of  the  nature  of  the 
starch  itself.  Even  the  addition  of  considerable  amounts  of  wax 
does  not  enable  it  to  take  so  good  a  finish  as  casein  coated  paper. 
This  does  not  prevent  half  tones  taking  well  on  it  for  its  surface 
is  sufficiently  smooth  and  even  to  print  well.  A  characteristic 
feature  of  starch  coated  paper  is  the  porosity  or  absorbent  power 
of  the  surface.  This  seems  to  be  greater  than  with  glue  or  casein 
coatings  so  that  the  printing  ink  tends  to  sink  in  rather  more  and 
the  resulting  cut,  especially  with  color  work,  is  slightly  dull. 


CLAY  345 

This  trouble  can  be  overcome  by  a  proper  adjustment  of  the  ink 
but  at  present  it  is  delaying  the  general  introduction  of  starch 
coating,  though  otherwise  the  paper  works  well,  running  well  on 
the  presses,  permitting  rapid  work  and  requiring  no  slip-sheeting. 

Miscellaneous  Adhesives.  Other  materials  have  been  pro- 
posed from  time  to  time  as  assistants  to,  or  substitutes  for,  casein 
and  among  these  may  be  mentioned  glutin,  viscose,  shellac, 
algae,  vegetable  gums,  mucilages,  etc.  While  these  may  be,  and 
probably  are,  used  in  small  quantities  or  for  special  purposes,  as 
for  instance  shellac  in  the  manufacture  of  imitation  leather 
papers,  their  employment  is  by  no  means  general  and  it  is  not 
probable  that  they  will  ever  seriously  compete  with  casein. 

Clay  The  nature  and  properties  of  clay  have  been  discussed 
in  the  chapter  on  fillers  and  the  methods  of  testing  which  are 
given  there  apply  equally  well  to  coating  clays.  The  principal 
differences  between  filler  and  coating  clays  are  in  color  and  fine- 
ness, the  coating  grades  being  whiter  and  finer  and  containing  less 
grit.  These  differences  are  not  by  any  means  along  hard  and 
fast  lines  since  the  higher  grade  filler  clays  are  sometimes  used  for 
coating,  while  for  certain  kinds  of  high  class  book  papers,  good 
grades  of  coating  clay  are  used  in  the  beating  engines.  The 
presence  of  grit  in  clay  for  coating  is  more  serious  than  in  a  filler 
since  it  is  sure  to  appear  on  the  surface  of  the  paper  where  it  inter- 
feres with  the  finish  and  may  even  cause  trouble  in  printing, 
especially  in  lithographing.  In  this  process  it  is  said  to  etch  the 
stones  or  plates  so  that  the  portions  which  should  remain  white 
are  not  entirely  ink  resistant  thus  permitting  the  ink  to  be  trans- 
ferred to  the  paper  when  it  is  not  desired  and  giving  tinted  or 
mottled  backgrounds. 

The  fineness  of  the  clay  has  a  large  influence  on  the  finish  which 
the  paper  will  take  on  calendering,  the  finer  the  particles  of  the 
clay  the  higher  the  gloss  which  is  imparted.  Unfortunately  the 
amount  of  casein,  or  other  adhesive,  required  increases  quite 
rapidly  as  the  size  of  the  clay  particles  decreases  so  that  the  gain 
in  finish  due  to  a  fine  clay  is  in  part  offset  by  the  effect  of  more 
adhesive.  Unexpected  or  unknown  changes  in  the  fineness  of 


346  COATED   PAPERS 

the  clays  used  are  without  doubt  responsible  for  some  of  the  cases 
of  weak  coating,  especially  when  the  amount  of  casein  used  is 
kept  as  near  the  minimum  as  possible. 

With  ordinary  clays  from  15  to  18  parts  of  casein  are  required 
for  100  parts  of  clay  and  with  this  casein  any  of  the  ordinary 
solvents  as  borax,  soda  ash,  ammonia  or  mixtures  of  these 
solvents  may  be  used  with  good  results. 

Blanc  Fixe  and  Barytes.  Both  of  these  are  chemically  barium 
sulphate,  BaS04;  blanc  fixe  being  prepared  by  precipitation 
while  barytes  is  the  natural  mineral  ground  and  bolted  to  any 
desired  degree  of  fineness.  The  best  grades  of  blanc  fixe  are 
prepared  from  witherite  (BaCOs)  by  dissolving  in  muriatic  acid, 
filtering  and  precipitating  with  sulphuric  acid.  The  precipitate 
is  washed  practically  free  from  acid  and  put  on  the  market 
either  dry  or  as  a  paste  containing  25  to  30  per  cent  of  moisture. 
Cheaper  grades  of  blanc  fixe  are  produced  as  by-products  in  the 
manufacture  of  hydrogen  peroxide,  etc.,  and  appear  to  be  only 
slightly  inferior  to  that  from  witherite  in  color  and  cleanliness. 
Under  the  microscope  blanc  fixe  is  seen  to  consist  of  extremely 
fine  crystals,  which  are  very  uniform  in  size.  If  large  irregular 
shaped  pieces  are  present  it  may  be  taken  as  an  indication  of 
adulteration  with  barytes  or  of  very  careless  handling  of  the 
solutions  before  precipitation.  The  grit  in  blanc  fixe,  as 
determined  by  the  flotation  test  described  in  the  chapter  on 
fillers,  should  not  exceed  0.2  to  0.3  per  cent  and  it  should  con- 
sist almost  entirely  of  small  lamps  of  the  blanc  fixe  itself  which 
have  not  broken  down  during  the  test.  This  test  also  will  show 
the  presence  of  barytes  though  not  its  amount.  The  reaction  of 
blanc  fixe  varies  commercially  from  neutral  to  decidedly  acid; 
both  appear  to  give  equally  good  results  under  ordinary  working 
conditions  as  the  acid  is  neutralized  by  the  excess  of  alkali  in  the 
casein. 

Barytes,  being  a  ground  mineral,  gives  much  larger  amounts 
of  grit  than  blanc  fixe,  the  flotation  test  showing  from  8  to  15  per 
cent  for  different  commercial  grades.  Its  particles  are  much 
coarser  and  more  variable  in  size  than  those  of  blanc  fixe,  and 


SATIN  WHITE 


347 


it  is  usually  quite  inferior  to  the  latter  in  color.  For  these  reasons 
it  should  not  be  used  in  the  highest  class  of  papers. 

Blanc  fixe  is  one  of  the  whitest  of  the  minerals  used  in  coating 
paper  and  can  be  used  in  the  very  best  of  products.  It  does  not 
take  such  a  high  finish  as  clay  or  satin  white  and  is  especially 
serviceable  in  making  dull  finish  coateds  since  it  has  less  tendency 
to  scratch  than  clay  or  satin  white.  Since  barium  sulphate  is 
practically  insoluble  it  cannot  react  with  casein  solutions  so  that 
almost  any  solvent  can  be  used  in  preparing  the  latter.  Both 
blanc  fixe  and  barytes  require  much  less  casein  than  does  clay  and 
both  tend  to  settle  out  of  the  coating  mixture  more  rapidly  than 
clay  on  account  of  their  high  specific  gravity. 

Satin  White.  This  material  consists  essentially  of  calcium 
sulphate  and  aluminum  hydrate,  formed  by  the  interaction  of 
slaked  lime  and  aluminum  sulphate;  3  Ca  (OH)2  +  A12  (864)3 
=  3  CaSO4  +  A12  (OH) 6.  The  alum  used  may  be  potash  or 
ammonia,  or  aluminum  sulphate  itself  may  be  used,  and  the 
character  of  the  resulting  product  depends  very  largely  on  which 
is  employed.  The  slaked  lime  is  frequently  used  in  excess  and 
the  amount  of  this  excess  together  with  the  quality  of  the  lime 
has  a  very  great  influence  on  the  working  properties  and  color 
of  the  product.  The  following  analyses  of  two  commercial  sam- 
ples of  satin  white  show  its  approximate  composition  after  .being 
dried  at  100°  C. 


No.  i 

No.  2 

Sulphur  trioxide,  SOs  

Per  cent 
28  Q 

Per  cent 
2Q    a 

Alumina,  AlzOa  

13   Q 

12    3 

Total  lime,  CaO  

3Q   I 

7Q.7 

Loss  on  ignition  

17  .  c 

l8.5 

99-4 

99-8 

Both  these  samples  contained  24  to  26  per  cent  of  free  lime 
while  other  samples  tested  for  this  substance  have  shown  that 
it  may  run  as  high  as  30  per  cent,  or  the  satin  white  may  even 
be  perfectly  neutral. 


348  COATED  PAPERS 

In  the  commercial  preparation  of  satin  white  the  slaked  lime 
is  mixed  with  alum  solution,  or  in  some  cases  the  undissolved 
alum,  and  after  sufficient  agitation  to  insure  a  uniform  reaction 
the  paste  is  diluted,  strained  through  fine  wire  gauze,  130  to  140 
mesh,  and  run  into  a  filter  press  where  it  is  washed  with  clear 
water.  The  resulting  paste  containing  about  30  per  cent  of  bone 
dry  material  is  the  satin  white  of  commerce.  When  a  standard 
method  of  manufacture  has  once  been  established  it  should  be 
strictly  adhered  to,  since  changes  in  the  kind  or  proportions  of 
the  ingredients  may  cause  differences  which  may  not  appear  in 
the  analysis  yet  which  will  cause  serious  trouble  in  the  coating 
room.  In  fact  it  cannot  be  safely  predicted  from  the  analysis 
how  a  lot  will  work  and  the  only  sure  way  is  to  give  it  a  trial  on  a 
practical  scale. 

The  properties  imparted  to  coated  paper  by  satin  white  are 
high  gloss  on  calendering  and  clear  white  color.  Because  of  the 
presence  of  aluminum  hydrate  the  coating  becomes  rather  dense 
and  brittle  so  that  papers  with  much  satin  white  have  rather 
poor  folding  qualities;  this  is  especially  true  with  very  heavily 
coated  papers. 

The  amount  of  casein  required  to  hold  a  given  amount  of  satin 
white  is  much  greater  than  for  the  same  amount  of  clay,  prob- 
ably in  most  cases  nearly  one  and  one  half  times  as  much.  Special 
precautions  have  to  be  used  in  mixing  the  two  or  the  result  is 
a  thick,  curdled  mass  which  cannot  be  spread.  In  order  to  avoid 
this  difficulty  the  casein  solution  may  be  prepared  with  an  ex- 
cess of  soda  ash  or  with  a  mixture  of  sodium  phosphate  and 
ammonia  and  the  satin  white  "should  be  mixed  with  a  little 
ammonia  before  the  casein  is  added.  When  phosphates  are 
present  with  satin  white  heating  causes  thickening  so  that  hot 
casein  solution  should  not  be  mixed  with  satin  white,  nor 
should,  the  mixture  be  heated.  For  working  with  this  material 
temperatures  of  30°  C.  or  below  are  desirable.  If  these  precau- 
tions are  observed  very  little  trouble  will  be  encountered. 

Accessories.  Under  this  heading  may  be  mentioned  those 
materials  which  are  used  in  small  amounts  or  for  special  pur- 


ACCESSORIES  349 

poses  and  which  do  not  form  an  essential  part  of  the  coating 
itself. 

(Soaps  and  waxes  are  added  for  the  purpose  of  improving  the 
finish  obtained  on  calendering.  Among  those  used  may  be  men- 
tioned, beeswax,  carnauba  wax,  stearic  acid,  paraffin,  Japan  wax, 
white  soap,  lard  oil,  etc.  Many  different  recipes  are  used  for 
mixing  the  ingredients  but  most  of  them  are  suspensions  or 
emulsions  of  one  or  more  substances  in  a  soapy  medium.  Japan 
wax  has  the  property  of  saponifying  very  readily  and  is  quite 
generally  used  to  hold  the  other  materials  in  suspension.  As  an 
example  of  this  type  the  following  formula  may  be  cited;  to 
about  250  gals,  of  hot  water  add  50  Ibs.  each  of  Japan  wax,  para- 
ffin and  stearic  acid  and  then  22  Ibs.  borax  and  a  little  ammonia. 
When  stirred  until  the  waxes  are  melted  this  forms  a  creamy  white 
permanent  emulsion  which  is  ready  to  use  in  the  coating  mixture. 

While  it  is  undoubtedly  true  that  such  materials  assist  in 
obtaining  the  high  finish  on  glace  papers  repeated  trials  have 
demonstrated  that  they  are  of  doubtful  value  for  the  ordinary 
grades  of  coated  papers  and  it  has  been  proved  that  at  times 
some  of  them  may  be  responsible  for  poor  results  in  printing. 

Closely  connected  with  this  class  of  materials  are  those  added 
to  prevent  undue  frothing  of  the  coating  mixture;  in  fact  some 
of  the  substances  sold  to  improve  the  finish  are  also  claimed  to 
reduce  the  froth.  Anti-frothing  substances  may  have  widely 
different  characteristics  as  for  instance  wood  alcohol,  Turkey  red 
oil,  fusel  oil,  skim  milk,  and  gasoline.  Probably  no  one  of  these 
will  work  in  every  case  as  froth  varies  in  its  character  and  cause 
but  it  is  believed  that  a  little  gasoline  added  to  the  frothing  mix- 
ture from  time  to  time  will  give  the  best  results.  This  sub- 
stance should  be  used  with  great  caution  on  account  of  the  danger 
of  fire. 

For  softening  the  coating  and  increasing  its  pliability  glycerine 
is  frequently  recommended.  Its  beneficial  effect  is  supposed  to 
be  due  to  its  hygroscopic  nature  but  tests  have  shown  that  com- 
mercial glycerines  absorb  very  little  moisture  from  the  air  so  that 
the  increase  in  weight  of  the  paper  would  be  practically  only  that 


350 

of  the  glycerine  added.  Tests  by  a  large  manufacturer  indicate 
that  amounts  up  to  2  per  cent  of  the  weight  of  dry  clay  in  the 
coating  have  practically  no  effect  on  the  folding  properties  of  the 
coated  paper  and  if  5  per  cent  is  used  the  printing  qualities  of  the 
paper  are  seriously  injured. 

The  glycerine  substitutes,  mostly  invert  sugars,  are  even  less 
hygroscopic  than  glycerine  itself  and  hence  would  have  even  less 
effect.  The  use  of  any  of  these  substances  is  therefore  of  doubt- 
ful advantage  and  their  use  is  not  to  be  recommended. 


CHAPTER  XIII 
WATER 

Water  which  is  pure,  in  the  sense  that  it  contains  no  foreign 

matter  of  any  kind,  is  never  found  in  nature,  so  that  from  the 
manufacturing  standpoint,  as  well  as  from  that  of  sanitation, 
water  must  be  considered  with  reference  to  the  amount  and 
kind  of  the  impurities  which  it  contains.  These  may  include 
solid,  liquid  or  gaseous  substances  and  they  may  be  either  in 
suspension  or  solution,  lioth  mineral,  or  inorganic  substances, 
and  organic  materials  may  be  present,  and  the  latter  may  be 
derived  from  decaying  vegetation  or  from  minute  living  organ- 
isms. Some  of  these  substances  may  have  a  great  influence  on 
the  quality  of  the  paper,  while  others,  which  are  harmless  for 
this  purpose,  are  decidedly  bad  if  used  in  boilers.  The  quality 
of  the  available  water  supply  is  therefore  a  vital  consideration 
in  connection  with  the  manufacture  of  paper. 

The  comparative  readiness  wit.li  which  the  quality  of  the 
water  affects  that  of  the  paper  is  still  further  emphasized  by  a 
consideration  of  (he  very  large  volumes  necessarv  for  the  vari- 
ous manufacturing  operations.  Griffin  and  Little  l  estimate  the 
amount  required  in  making  a  ton  of  paper  at  50,000  to  200,000 
gals.,  or  about  200  to  800  times  the  weight  of  the  paper  pro- 
duced. Others  have  estimated  that  in  American  line  paper 
mills,  making  linens,  bonds  and  ledgers  from  rag  stock,  the 
water  used  Amounts  to  1000  gals,  per  pound  of  dry  paper  made.2 
Reliable  data  for  water  consumption  are  rarely  available  and 
no  generally  applicable  figures  can  be  given  because  its  use 
depends  so  largely  on  local  conditions,  as  purity,  quantity  avail- 

1    < 'lii-mis!  ry  of  I'aprr  Making,  p. 

9  Paper:  June  21,  1916,  p.  12. 


352  WATER 

able,  cost  of  pumping,  necessity  for  nitration,  reuse  of  back- 
water, etc.  In  some  cases  it  may  be  necessary  to  purify  the 
waste  waters  in  order  to  avoid  stream  pollution  and  this  tends 
to  reduce  the  amount  of  water  used.  Considering  these  enor- 
mous volumes,  and  the  fact  that  the  paper  stock  forms  a  very 
effective  filter,  the  result  of  very  small  amounts  of  injurious  sub- 
stances may  be  easily  imagined.  Compared  with  this  problem 
that  of  the  boiler-house  supply  for  steam  raising  is  relatively 
unimportant. 

Waters  may  be  broadly  classified  as  (i)  rain,  (2)  surface  and 
(3)  ground  waters.  Rain  water,  if  properly  collected,  is  the 
purest  form  of  natural  water,  though  it  always  contains  gases 
and  impurities  from  roofs,  products  of  combustion,  etc.  Be- 
cause of  the  relatively  small  amounts  available  it  is  of  no  prac- 
tical importance  as  a  paper  making  supply.  Surface  waters 
include  those  of  brooks,  rivers,  ponds  and  lakes.  These  waters 
pick  up  impurities  of  various  kinds  according  to  the  nature  of 
the  soils  over  which  they  flow  and  they  are  also  contaminated 
by  mineral  substances  derived  from  springs  which  discharge 
into  them.  They  generally  contain  less  mineral  matter  but 
more  organic  matter  than  ground  waters,  and,  particularly  in 
the  case  of  river  waters,  are  likely  to  vary  greatly  in  composi- 
tion at  different  periods  of  the  year.  Suspended  matter  is  usu- 
ally present  in  greater  or  less  amount  and  in  the  case  of  swamp 
waters  there  is  usually  a  yellowish  color  due  to  the  peaty  soil 
over  which  the  water  has  passed.  Waters  of  this  type  are 
likely  to  contain  plant  and  animal  life  which  may  impart  con- 
siderable color  to  them.  Ground  waters  are  those  which  have 
percolated  through  a  considerable  depth  of  soil  and  the  under- 
lying porous  strata.  Such  waters,  derived  from  springs  and 
deep  wells,  are  usually  clear  and  colorless  but  they  contain 
more  dissolved  mineral  matter  than  do  surface  waters. 

Soft  waters  are  those  which  contain  little  of  those  mineral 
substances  which  are  capable  of  decomposing  soap,  while  hard 
waters  are  those  which  possess  this  property  to  a  marked  de- 
gree. The  most  common  cause  of  hardness  is  the  presence  of 


WATER  353 

lime  salts,  either  the  sulphate  or  carbonate,  the  latter  being 
much  the  more  general.  The  salts  of  magnesium  have  an  even 
greater  effect  than  those  of  calcium  but  they  are  not  so  often 
present.  The  sulphates  of  both  calcium  and  magnesium  are 
soluble  in  pure  water  but  the  carbonates  require  the  presence 
of  carbon  dioxide  to  enable  them  to  dissolve  as  bicarbonates. 
The  necessary  carbon  dioxide  is  derived  from  the  air,  from  the 
decay  of  vegetable  matter  or  from  subterranean  sources.  Bicar- 
bonates form  what  is  termed  " temporary  hardness"  since  on 
boiling  the  carbon  dioxide  is  driven  off,  causing  the  precipita- 
tion of  calcium  carbonate  and  the  softening  of  the  water.  Sul- 
phates cause  " permanent  hardness"  since  they  are  not  apected 
by  boiling. 

Soft  water  is  said  to  be  desirable  for  the  washing  of  stock 
because  it  has  a  greater  solvent  power  than  hard  water.  If  the 
latter  is  employed  for  washing  sulphite  fibre  there  is  a  tendency 
for  insoluble  calcium  resinates  to  be  deposited  on  the  fibre, 
thus  rendering  the  product  unnecessarily  hard  to  bleach,  while 
in  the  soda  process  the  lime  salts  may  be  precipitated  as  car- 
bonate or  sulphate  and  carry  down  coloring  matters  with  the 
same  result.1  Water  which  is  very  hard  because  of  the  pres- 
ence of  calcium  bicarbonate  may  also  be  injurious  to  sizing, 
though  the  presence  of  calcium  sulphate  is  harmless.  For  other 
purposes  in  paper  making  as  in  the  boiling  of  either  sulphite, 
soda  or  rag  stock,  or  in  bleaching,  or  furnishing  an  engine,  the 
importance  of  soft  water  is  greatly  overestimated  since  the 
materials  employed  will  immediately  harden  the  softest  water. 

In  making  colored  papers  the  quality  of  the  water  may  affect 
the  results  obtained.  Carbonates  cause  precipitation  of  the 
salts  of  iron,  tin  and  aluminum,  which  are  sometimes  used  as 
mordants,  and  reduce  their  effectiveness.  Sulphates  have  little 
or  no  action.  Neither  carbonate  nor  sulphate  will  cause  trouble 
when  using  acid  colors  as  the  amount  of  acid  used  far  outweighs 
any  alkali  present  in  the  water.  Iron  in  the  water  dulls  almost 
all  mordant  colors.  It  is  also  very  injurious  in  the  manufac- 

1  Beveridge:  Paper,  Oct.  30,  1918. 


354  WATER 

ture  of  photographic  paper,  particularly  if  it  is  present  in  such 
form  that  it  may  deposit  in  the  pipes,  reservoirs,  etc.,  as  such 
sludge  may  break  away  at  times  and  cause  endless  trouble.1 

The  most  important  quality  of  water,  from  a  paper  making 
point  of  view,  is  its  color.  The  purest  natural  waters  are  clear 
and  colorless  when  examined  in  comparatively  thin  layers,  while 
in  large  masses  they  have  a  bluish  tint.  Surface  waters  on  the 
other  hand  show  all  variations  in  color  from  colorless,  through 
yellowish  and  reddish  tints,  to  the  deep  brown  of  swamp  water. 
This  color  is  due  largely  to  decaying  vegetable  matter  and 
where  the  decay  has  proceeded  far  the  color  is  very  permanent 
in  character.  The  color  derived  from  plant  growths,  princi- 
pally algae,  is  usually  most  pronounced  in  the  summer  months. 
They  are  green  or  bluish  green,  require  light  for  their  develop- 
ment and  thrive  best  in  ponds  or  reservoirs  where  there  is  little 
movement  to  the  water.  These  lower  forms  of  plant  life  are 
very  sensitive  to  copper  sulphate  and  a  treatment  with  a  very 
small  amount  of  this  material  is  sufficient  to  destroy  them. 
This  method  is  often  used,  even  in  the  case  of  a  water  supply  for 
drinking  purposes. 

At  tunes  the  color  of  a  water  is  greatly  affected  by  the  sus- 
pended matter  which  it  carries;  this  is  a  very  variable  factor, 
its  greatest  effect  appearing  when  heavy  rains  have  washed 
much  finely  divided  soil  into  the  streams.  Soluble  mineral 
matter  has,  as  a  rule,  little  effect  on  the  color,  even  the  soluble 
salts  of  iron  are  seldom  present  in  sufficient  concentration  to 
cause  any  perceptible  color.  Trouble  is  caused,  however,  when 
for  any  reason  these  iron  salts  are  precipitated  as  hydroxide. 

Practically  all  waters,  especially  surface  waters,  consume  small 
quantities  of  bleaching  powder,  the  amount  depending  upon 
the  source  of  the  water.  In  most  cases  the  loss  of  bleach  from 
this  cause  is  slight  but  if  much  organic  matter  is  present,  as  in 
swamp  waters  or  those  largely  contaminated  with  trade  wastes 
or  sewage,  the  loss  may  be  appreciable.  Griffin  and  Little 2 

1  Anon:  Paper,  Jan.  i,  1919. 

2  Chemistry  of  Paper  Making,  p.  333  (1894). 


BOILER   SCALE  355 

give  the  bleach  consumed  by  three  waters  as  1.77,  1.16  and  3.87 
grains  per  gallon  but  do  not  state  the  source  of  the  water  or  the 
conditions  of  the  test. 

Water  which  is  to  be  used  for  boiler  purposes  should  gener- 
ally be  soft  and  free  from  suspended  matter,  for  substances 
either  in  solution  or  suspension  will  accumulate  and  form  mud 
or  scale.  Such  a  deposit  may  be  hard  and  dense  or  loose  and 
porous  according  to  the  substances  present.  Dense  scale  is  the 
more  serious  and  water  which  causes  it  should  either  be  avoided 
or  treated  in  some  way.  Such  a  scale  causes  a  large  loss  of  fuel 
by  preventing  the  transfer  of  heat  to  the  water  and  when  it  is 
of  any  considerable  thickness  there  is  danger  of  overheating  the 
boiler  locally  with  consequent  damage  to  the  tubes  or  plates. 
Hardness,  however,  is  not  always  an  indication  of  scale  forming 
power  for  both  calcium  chloride  and  magnesium  sulphate  make 
water  hard  but  do  not  form  scale. 

One  of  the  most  frequent  causes  of  scale  is  calcium  carbonate. 
This  is  present  as  bicarbonate  but  at  the  temperature  of  the 
boiler  is  again  broken  down  into  calcium  carbonate  and  carbon 
dioxide.  This  same  reaction  takes  place  with  magnesium  bicar- 
bonate and  if  both  are  present  in  the  water  they  will  be  found 
together  in  the  scale.  The  precipitated  carbonates  are  at  first 
loose  and  powdery  but  if  the  boiler  is  blown  off  without  cooling 
the  flues,  the  precipitate  is  likely  to  bake  into  a  dense,  hard 
scale.  Under  these  conditions  the  magnesium  appears  in  the 
scale  as  hydroxide.  Calcium  carbonate  is  not  so  likely  to  bake 
onto  the  plates  as  the  magnesium  salt.  The  following  analysis  x 
shows  the  general  characteristics  of  a  carbonate  scale,  though 
the  relative  proportions  are  likely  to  vary  quite  widely  in 
different  samples. 

Per  cent  Per  cent 

Carbonate  of  lime 75-85        Silica 7. 66 

Sulphate  of  lime 3-68        Oxides  of  iron  and  alumina       2. 96 

Hydrate  of  magnesia 2.  56        Organic  matter 3-64 

Chloride  of  sodium o.  45        Moisture . 3.  20 

100.00 

1  Griffin  and  Little:  Chemistry  of  Paper  Making,  p.  334  (1894). 


356 


WATER 


If  the  hardness  of  a  water  is  due  to  calcium  sulphate  no  pre- 
cipitation takes  place  until  the  solution  becomes  saturated  due 
to  concentration;  then  a  crystalline  scale  deposits.  This  is  at 
first  CaSO4  •  2  H2O,  but  it  begins  to  lose  its  water  of  crystal- 
lization at  about  260°  F.  and  becomes  more  insoluble.  These 
actions  tend  to  produce  a  hard  scale  which  may  accumulate  to 
a  considerable  thickness. 

A  certain  amount  of  scale  may  be  formed  in  the  boilers  even 
when  the  water  is  soft,  though  the  quantity  is  almost  never 
enough  to  be  serious.  The  following  analyses  show  the  com- 
position of  a  soft  water  which  proved  excellent  for  boiler  pur- 
poses and  also  of  the  scale  which  formed  during  its  use. 

WATER* 


Constituents 

Parts  per 
million 

Per  cent  of 
dry  matter 

Silica  (SiO2) 

3   8 

I  S    <J 

Iron  (Fe) 

O   O4. 

O    2 

Calcium  (Ca) 

32 

1  3     I 

Magnesium  (Mg) 

o  6 

2    A 

Sodium  and  potassium  (Na  -j-  K)  ....    . 

4    2 

17    I 

Carbonate  radicle  (COO  

O   O 

28    ^ 

Bicarbonate  radicle  (HCOs)  

14.0 

Sulphate  radicle  (SO4)  
Nitrate  radicle  (NO3)  

3-6 
o.  q 

14-7 
2    O 

Chlorine  (Cl)     

1.6 

6  5 

Total  suspended  solids 

7   4. 

Total  dissolved  solids 

2<?    O 

SCALE 


M^oisture  and  organic  matter 

Per  cent 
17    16 

Silica  (SiO2)  

35  -64 

Ferric  oxide  (Fe2Oa)                                         ...        .    . 

4  •  32 

Alumina  (AUOs)                        .             

4.28 

Calcium  oxide  (CaO)  .  .      .        

30.97 

Magnesium  oxide  (MgO)  

5  -59 

Carbon  dioxide  (CC>2) 

i  40 

Sulphur  trioxide  (SOs)  

0.92 

100  .  28 

*  Analysis  by  U.  S.  Geological  Survey. 

Water  Softening.     Many  so-called  "boiler  compounds"  have 
been  proposed  for  use  in  the  prevention  of  scale  and  while  some 


WATER   SOFTENING  357 

may  work  well  under  certain  conditions,  none  are  of  universal 
application  and  many  are  useless  or  even  injurious.  If  the 
water  is  bad  enough  so  that  a  " boiler  compound"  seems  de- 
sirable, it  is  in  most  cases  preferable  to  give  it  a  preliminary 
softening  treatment. 

For  waters  containing  the  bicarbonates  of  calcium  and  mag- 
nesium the  method  most  generally  employed  is  that  of  Clark, 
which  consists  in  adding  slaked  lime  to  react  according  to  the 
equation : 

CaH2(C03)2  +  Ca(OH)2  =  2  CaC03  +  2  H2O 

The  lime  is  added  either  as  lime  water  or  milk  of  lime,  the 
former  being  preferable  because  it  is  more  easy  to  control. 
This  treatment  removes  all  the  bicarbonate  as  well  as  the  added 
lime. 

This  method  was  originally  applied  in  large  tanks  where  the 
water  could  remain  quiescent  for  a  considerable  time.  The 
lime  water  was  added  in  such  an  amount  that,  after  thorough 
mixing,  the  water  gave  a  yellow  or  brown  color  with  silver 
nitrate,  then  more  water  was  added  until  the  silver  nitrate 
test  gave  no  color.  This  test  should  always  be  applied  in  order 
to  make  sure  that  an  excess  or  deficiency  of  lime  is  not  caused 
by  variation  in  the  water  supply.  Temporary  hardness  of 
course  is  all'  that  is  removed,  and  even  that  not  completely,  as 
a  little  calcium  carbonate  remains  in  solution  and  magnesium 
bicarbonate  is  not  so  completely  removed  as  that  of  calcium. 
Salts  of  iron  and  some  organic  matter  are  also  removed. 

Various  modifications  of  this  process  have  been  tried  out  in 
the  attempt  to  shorten,  or  do  away  with,  the  time  required  for 
settling.  The  Porter-Clark  process  employs  a  filter  press  for 
the  removal  of  the  precipitate.  Gaillet  and  Huet  cause  the 
water  to  take  a  zig-zag  course  to  promote  sedimentation  and 
often  use  both  lime  and  caustic  soda  to  remove  both  temporary 
and  permanent  hardness  according  to  the  reactions 

CaH2(CO3)2  +  2NaOH  =  CaC03  +  Na2CO3  +  2  H20, 
CaSO4  +  Na2CO3  =  CaCO3  +  Na2SO4. 


358  WATER 

The  Archbutt-Deeley  process  blows  air  through  the  treated 
water  after  mixing  it  with  the  sludge  from  a  previous  precipi- 
tation. This  hastens  the  sedimentation  so  that  the  clear  water 
may  be  drawn  from  the  top  by  a  floating  arm.  Other  proposed 
modifications  employ  barium  hydroxide,  sodium  oxalate,  mag- 
nesium hydroxide,  etc.  The  latter  is  not  always  to  be  recom- 
mended as  it  may  result  in  the  formation  of  magnesium  chloride 
and  consequent  corrosion  of  the  boiler. 

An  entirely  different  process  is  the  so-called  permutite  pro- 
cess. Permutite  is  an  artificial  zeolite  formed  by  fusing  together 
silica,  alumina  or  china  clay,  and  sodium  carbonate.  On  ex- 
traction with  water  a  crystalline  body  is  obtained  of  the  approxi- 
mate composition,  SiO2,  46;  A1203,  22;  Na2O,  13.6;  H20,  18.4. 
Filtration  of  water  through  this  material  removes  the  calcium 
and  magnesium  thus: 

Na2Al2Si2O8  +  CaCO3  =  Na2CO3  +  CaAl2Si2O8, 
Na2Al2Si2O8  +  CaSO4  =  Na2SO4 


It  is  claimed  that  the  whole  of  the  hardness  is  removed  and 
that  the  calcium  and  magnesium  zeolites  formed  can  be  recon- 
verted into  the  original  permutite  by  treating  with  a  strong 
solution  of  salt.  A  manganese  permutite  can  also  be  used  for 
the  removal  of  iron. 

Filtration.  The  principal  action  in  filtering  water  is  that  of 
straining  to  remove  suspended  mineral  and  vegetable  matter. 
It  is,  however,  much  more  complex  than  a  mere  straining  since 
the  water  undergoes  chemical  and  biological  changes,  particu- 
larly in  slow  sand-filtration.  Among  these  changes  oxidation 
is  one  of  the  chief,  due  to  the  fact  that  in  passing  through  porous 
earth  an  enormous  surface  is  exposed.  In  natural  filtration, 
during  the  transformation  of  surface  into  ground  waters,  this 
action  may  proceed  so  far  that  all  the  organic  matter  originally 
present  is  oxidized  leaving  the  water  clear  and  colorless.  In 
continuous  mechanical  filtration  no  such  oxidation  takes  place  and 
the  removal  of  organic  matter  has  to  be  secured  by  other  means. 

Many  forms  of  mechanical  filters  have  been  devised,  some 


WATER  ANALYSIS  359 

working  by  gravity  and  some  under  pressure.  With  all  of  them 
some  provision  is  made  for  cleaning  the  filtering  medium,  which 
is  usually  sand,  either  by  reversing  the  flow  of  water,  by  me- 
chanical agitation  with  rakes,  by  compressed  air  or  some  other 
means.  The  frequency  of  such  cleaning  depends  on  the  quality 
of  the  water,  and  if  this  varies  much,  due  to  the  time  of  year, 
storms,  etc.,  the  intervals  between  cleaning  will  also  vary.  If 
the  stream  from  which  the  water  is  drawn  is  contaminated  with 
fibre,  sawdust  or  other  coarse  mechanical  impurities  the  effi- 
ciency of  the  filters  may  be  greatly  increased  by  first  running 
the  water  supply  over  a  revolving  screen  similar  to  the  moulds 
of  a  wet  machine. 

Water  may  be  filtered  directly,  in  which  case  only  suspended 
matter  will  be  removed,  or  it  may  first  be  treated  with  a  little 
alum.  The  slight  alkalinity  of  most  waters  causes  the  precipi- 
tation of  hydrated  alumina  which  on  standing  for  some  time 
collects  in  flocks  of  appreciable  size,  gathers  together  finely 
divided  suspended  matter  and  at  the  same  time  takes  out  much 
of  the  organic  coloring  matter.  The  precipitate  forms  a  film 
over  the  filtering  medium  and  aids  in  removing  bacteria  and 
other  minute  organisms.  If  much  loam  or  silt  is  present  a 
little  lime  is  sometimes  added  before  the  alum  to  insure  a  suffi- 
ciently bulky  precipitate.  The  amount  of  alum  necessary  de- 
pends on  the  hardness  of  the  water.  It  is  customary  to  add 
it  mechanically  by  some  sort  of  device  controlled  by  the  flow 
of  the  raw  water  so  that  the  proportion  added  may  be  the  same 
at  all  times.  After  the  addition  of  the  alum  it  is  desirable  that 
the  water  remain  for  thirty  minutes  to  an  hour  in  a  settling 
basin  where  heavy  sediment  may  settle  and  the  chemical  reac- 
tion between  the  alum  and  the  bases  present  in  the  water  may 
take  place.  It  is  then  ready  to  pass  to  the  filter. 

Water  Analysis.  The  following  analytical  methods  have  been 
taken  in  large  part  from  "  Standard  Methods  for  the  Examina- 
tion of  Water  and  Sewage,"  x  to  which  reference  should  be 
made  if  more  complete  details  are  desired. 

1  Am.  Public  Health  Assn.,  Boston,  1917. 


360       .  WATER 

Sampling.  Care  must  be  taken  that  the  sample  is  truly  rep- 
resentative of  the  liquid  to  be  analyzed.  If  for  any  reason 
variations  are  likely  to  occur,  as  for  instance  because  of  periodic 
contamination  by  trade  waste,  a  sample  obtained  by  mixing 
together  several  portions  taken  at  different  times  is  likely  to 
be  more  representative  than  one  taken  all  at  one  time.  The 
amount  required  for  the  ordinary  chemical,  physical  and  micro- 
scopical analysis  is  not  less  than  two  liters,  and  for  special  tests 
larger  quantities  may  be  required. 

The  samples  should  be  collected  in  glass-stoppered  bottles 
which  have  been  previously  cleaned  with  sulphuric  acid  and 
potassium  bichromate  or  with  alkaline  permanganate,  followed 
by  a  mixture  of  oxalic  acid  and  sulphuric  acid  and  by  thorough 
rinsing  and  draining.  The  stoppers  and  necks  of  the  bottles 
should  be  protected  from  dirt  by  tying  cloth  or  thick  paper 
over  them. 

The  time  which  may  safely  elapse  between  the  collection  of 
the  sample  and  its  analysis  depends  on  the  character  of  the 
sample  and  the  tests  to  be  made.  No  exact  limits  can  be  fixed 
but  it  is  considered  that  the  analysis  should  be  begun  within 
the  following  times. 


Physical  and 
chemical  analyses 

Microscopic 
examinations 

Ground  waters  

Hours 
72 

Hours 
72 

Fairly  pure  surface  waters  

48 

24 

Polluted  surface  waters  

12 

In  general  the  shorter  the  time  elapsing  between  the  collection 
of  a  sample  and  its  analysis  the  more  reliable  will  be  the  ana- 
lytical results. 

Turbidity.  The  turbidity  of  water  is  due  to  suspended  mat- 
ter such  as  clay,  silt,  finely  divided  organic  matter,  microscopic 
organisms,  etc. 

The  standard  for  turbidity  adopted  by  the  United  States 
Geological  Survey,1  is  a  water  containing  100  parts  per  million 

1  F.  D.  West:  Proc.  111.  Water  Supply  Assoc.,  Vol.  VT,  pp.  49~5i>  I9H- 


COLOR  361 

of  silica  in  such  a  state  of  fineness  that  a  bright  platinum  wire 
i  mm.  in  diameter  can  just  be  seen  when  the  centre  of  the  wire 
is  100  mm.  below  the  surface  of  the  water  and  the  eye  of  the 
observer  is  1.2  meters  above  the  wire.  This  observation  should 
be  made  in  the  middle  of  the  day,  in  the  open  air  but  not  in 
sunlight,  and  in  a  vessel  so  large  that  the  sides  do  not  shut  out 
the  light  so  as  to  influence  the  results.  The  standard  may  be 
prepared  by  sifting  dry  Pear's  "precipitated  fuller's  earth" 
through  a  2oo-mesh  sieve  and  suspending  i  gram  of  the  mate- 
rial in  i  liter  of  distilled  water.  This  has  a  turbidity  of  1000 
but  should  be  tested  by  diluting  with  nine  times  its  volume  of 
water  and  trying  out  with  the  platinum  wire  apparatus.  If  not 
exactly  right  it  may  be  adjusted  by  adding  more  silica  or  more 
water.  This  method  requires  a  rod  with  a  platinum  wire  i  mm. 
in  diameter  inserted  in  it  i  in.  from  one  end  and  projecting 
from  it  at  least  25  mm.  Near  the  other  end  of  the  rod  and  1.2 
meters  from  the  wire  is  fixed  a  small  ring,  directly  above  which 
the  observer  places  his  eye  when  making  the  observation.  This 
rod  is  graduated  so  that  when  lowered  into  the  water  to  be 
tested,  as  far  as  the  wire  can  be  seen,  the  level  of  the  water  on 
the  graduated  scale  indicates  the  turbidity. 

Turbidity  may  also  be  determined  by  the  candle  turbidi- 
meter,1  which  consists  of  graduated  glass  tubes  with  flat  pol- 
ished bottoms,  enclosed  in  a  metal  case.  This  is  supported 
over  an  English  standard  candle  so  that  the  distance  from  the 
bottom  of  the  tube  to  the  top  rim  of  the  candle  shall  be  3  ins. 
The  observation  is  made  by  pouring  the  sample  of  water  into 
the  tube  until  the  image  of  the  candle  flame  just  disappears. 
This  test  should  be  carried  out  in  a  darkened  room  or  with  a 
black  cloth  over  the  head.  An  electric  light  may  conveniently 
be  substituted  for  the  candle  as  it  avoids  any  deposit  of  soot 
or  moisture  on  the  tubes.  The  calibration  of  the  instrument 
may  be  made  by  means  of  the  silica  standards  already  mentioned. 

Color.  The  "true  color"  of  water  is  that  due  to  substances 
in  solution  while  the  "apparent  color"  is  that  of  the  original 

1  Tech.  Quart.,  Vol.  XIII,  pp.  274-279,  1900. 


362  WATER 

unfiltered  sample  and  includes  also  any  color  caused  by  sus- 
pended matter. 

A  convenient  standard  for  color  1  is  prepared  by  dissolving 
1.246  grams  of  potassium  platinic  chloride  (PtCl4  •  2  KC1),  con- 
taining 0.5  gram  of  platinum,  and  i  gram  crystallized  Cobalt 
chloride  (CoQ2  •  6  H2O) ,  containing  0.25  gram  of  cobalt,  in 
water  with  100  c.c.  concentrated  hydrochloric  acid  and  diluting 
to  i  liter  with  distilled  water.  This  solution  has  a  color  of  500 
and  by  diluting  in  Nessler  tubes  standards  of  o,  5,  10,  15,  20, 
25>  3°>  35?  4°>  5°>  60  and  7°  should  be  prepared.  These  tubes 
should  be  of  such  diameter  that  the  graduation  mark  is  20  to 
25  cm.  above  the  bottom  and  of  such  uniformity  that  the  dis- 
tance from  the  bottom  to  the  graduation  of  the  longest  tube 
shall  not  be  more  than  6  mm.  greater  than  that  of  the  shortest 
tube.  The  tubes  should  be  protected  from  light  and  dust  when 
not  in  use. 

The  color  of  the  sample  is  measured  by  rilling  a  standard 
Nessler  tube  to  the  height  equal  to  that  in  the  standard  and 
then  comparing  by  looking  vertically  downward  through  the 
tubes  upon  a  white  surface  placed  at  such  an  angle  that  light 
is  reflected  upward  through  the  liquid.  Water  with  a  color 
greater  than  70  should  be  diluted  before  testing,  and  water  con- 
taining suspended  matter  should  be  filtered  unless  the  apparent 
color  is  desired,  in  which  case  unfiltered  water  should  be  used. 

Nitrogen.  This  occurs  in  water  in  various  forms  as  ammonia, 
nitrites,  nitrates,  etc.,  and  its  determination  has  been  standard- 
ized by  numerous  methods.  It  is  of  very  great  importance 
when  considering  water  from  a  Sanitary  standpoint,  as  its  pres- 
ence in  any  appreciable  quantity  indicates  pollution,  but  as  it 
is  of  minor  importance  in  the  manufacturing  operations  of 
paper  making  the  methods  for  its  determination  will  not  be 
discussed. 

Oxygen  Consumed.  This  is  determined  by  heating  100  c.c. 
of  the  water  with  10  c.c.  of  dilute  H2S04  and  10  c.c.  of  a  stand- 
ard solution  of  potassium  permanganate,  adding  10  c.c.  of  a 

1  Am.  Chem.  J.,  Vol.  XIV,  pp.  300-310,  1892. 


SUSPENDED   MATTER  363 

standard  ammonium  oxalate  solution  and  titrating  the  excess 
with  the  permanganate. 

It  is  considered  by  some  as  an  indication  of  the  amount  of 
carbonaceous  matter  present  but  where  pollution,  or  contami- 
nation with  trade  wastes,  has  taken  place  it  will  also  include 
such  materials  as  nitrite  nitrogen,  ferrous  iron,  sulphides,  etc. 

As  a  substitute  for  this  determination  it  is  suggested  that  a 
direct  determination  of  the  bleach  consumed  by  the  water  under 
conditions  of  temperature  and  time  similar  to  those  of  actual 
fibre  bleaching  operations  would  be  of  much  more  value  to  the 
paper  maker.  This  can  be  carried  out  by  adding  a  known  vol- 
ume of  a  standard  hypochlorite  solution  and  after  allowing  it  to 
stand  for  a  definite  time  determining  the  amount  remaining; 
the  difference  represents  the  amount  consumed. 

Residue  on  Evaporation.  Ignite  and  weigh  a  clean  platinum 
dish,  and  measure  into  it  100  c.c.  of  the  thoroughly  shaken 
sample.  Evaporate  to  dryness  on  the  water  bath,  heat  in  an 
oven  at  103°  C.  or  180°  C.  for  one  hour,  cool  in  a  desiccator 
and  weigh.  The  increase  in  weight  gives  the  total  solids  or 
residue  on  evaporation.  The  results  should  be  expressed  as 
parts  per  million  and  the  temperature  of  drying  should  be  given 
in  the  report. 

Fixed  Residue.  Ignite  the  total  solids  in  the  platinum  dish 
at  a  low  red  heat.  Cool,  moisten  the  residue  with  a  few  drops 
of  distilled  water,  dry  in  the  oven,  cool  in  a  desiccator  and 
weigh.  For  the  greatest  accuracy  an  electrically  heated  muffle 
furnace  should  be  used.  The  loss  on  ignition  is  the  difference 
between  the  total  residue  on  evaporation  and  the  fixed  residue 
on  evaporation. 

Suspended  Matter.  This  may  be  determined  directly  by 
means  of  an  asbestos  lined  Gooch  crucible  or  indirectly  by  cal- 
'culation  from  the  difference  between  the  total  solids  in  filtered 
and  unfiltered  portions  of  the  same  sample. 

A  test  which  gives  valuable  information  regarding  the  paper 
making  value  of  water  is  made  by  treating  a  definite  volume  of 
the  water  with  enough  dilute  aluminum  sulphate  solution  to 


364  WATER 

precipitate  all  coagulable  matter.  After  allowing  it  to  stand 
a  sufficient  time  for  coagulation  to  take  place,  it  is  filtered 
through  a  Gooch  crucible  or  through  a  tared  filter  paper  and 
the  weight  of  the  precipitate  determined  by  difference  after 
drying.  The  amount  and  character  of  the  precipitate  indicate 
whether  the  water  will  prove  satisfactory  without  filtration  or 
whether  it  will  be  necessary  to  treat  it  with  alum  and  filter 
before  using. 

Hardness.  A  water  is  said  to  be  hard  when  it  contains  in 
solution  mineral  constituents,  which  form  insoluble  compounds 
with  soap.  The  most  accurate  method  of  ascertaining  total 
hardness  is  to  calculate  it  from  the  amounts  of  calcium  and 
magnesium  found  by  analysis  of  the  sample.  If  appreciable 
amounts  of  iron  or  other  metals  are  present  these  must  be 
included  in  the  calculation.  The  total  hardness  expressed  as 
CaCO3  equals  2.5  Ca  plus  4.1  Mg. 

Titration  with  standard  soap  solution  is  a  method  often  em- 
ployed for  determining  total  hardness,  though  in  reality  it 
merely  measures  the  soap  consuming  power  of  the  water.  The 
soap  solution  is  prepared  by  dissolving  100  grams  of  dry,  white 
Castile  soap  in  i  liter  of  80  per  cent  alcohol.  After  standing 
several  days  dilute  100  c.c.  to  i  liter  with  70  per  cent  alcohol 
and  standardize  against  a  solution  of  calcium  chloride  contain- 
ing the  equivalent  of  0.2  gram  CaCO3  per  liter.  This  is  done  by 
placing  20  c.c.  of  calcium  chloride  solution  in  a  25o-c.c.  glass- 
stoppered  bottle  and  diluting  to  50  c.c.  with  distilled  water 
which  has  been  recently  boiled  and  cooled.  To  this  the  soap 
solution  is  added  from  a  burette,"  0.2  to  0.3  c.c.  at  a  time,  shak- 
ing vigorously  after  each  addition,  until  the  lather  remains 
unbroken  for  five  minutes  over  the  entire  surface  of  the  water 
while  the  bottle  lies  on  its  side.  Repeat  this  test,  using  15  c.c., 
10  c.c.  and  5  c.c.  of  the  calcium-chloride  solution  and  finally 
distilled  water  alone,  and  from  the  results  plot  a  curve  showing 
the  relation  of  various  quantities  of  soap  solution  to  correspond- 
ing quantities  of  calcium  carbonate  and  hence  to  parts  per 
miUion  of  hardness. 


IRON  365 

In  testing  water  50  c.c.  of  the  sample  are  placed  in  the  bottle 
and  the  test  carried  out  exactly  as  in  the  standardization  of  the 
soap  solution.  If  magnesium  is  present  a  false  end  point  may 
be  obtained.  To  see  if  this  is  the  case,  read  the  burette  when 
the  end  point  has  apparently  been  reached  and  then  add  0.5  c.c. 
more  of  the  soap  solution.  If  the  end  point  was  caused  by  mag- 
nesium the  lather  will  disappear  and  the  titration  must  be 
continued  until  the  true  end  point  is  reached. 

Temporary  Hardness.  Temporary  hardness  is  due  to  mag- 
nesium or  calcium  carbonates  which  are  held  in  solution  as 
bicarbonates  by  dissolved  carbon  dioxide,  and  which  are  partly 
precipitated  when  the  latter  is  driven  off  by  boiling.  It  is  most 
accurately  estimated  by  determining  the  alkalinity  by  titration 
with  N/5o  acid,  using  methyl  orange  as  indicator,  both  in  the 
original  water  and  again  after  boiling,  cooling,  making  up  to 
the  original  volume  with  boiled  distilled  water  and  filtering. 
The  difference  between  the  two  titrations  represents  temporary 
hardness  which  would  include  iron  bicarbonate. 

Alkalinity  or  Acidity.  Alkalinity  or  acidity  may  be  deter- 
mined by  titration  with  N/5o  acid  or  sodium  carbonate  re- 
spectively. Indicators  for  alkalinity  include  phenolphthalein, 
methyl  orange,  lacmoid  and  erythrosine  while  for  total  acidity 
phenolphthalein  should  be  used. 

Chlorides.  The  chlorides  in  water  are  due  to  common  salt, 
which  may  come  from  mineral  deposits  in  the  earth,  from  wind- 
borne  ocean  vapors  or  from  sewage  and  trade  wastes. 

It  may  be  determined  by  titrating  a  measured  volume  of  the 
water  with  standard  silver  nitrate,  using  chloride-free  potassium 
chromate  solution  as  indicator.  This  shows  a  faint  reddish 
color  when  the  end  point  is  reached.  If  the  water  has  a  color 
greater  than  30  it  should  be  decolorized  by  shaking  with  a  little 
washed  aluminum  hydroxide  and  allowing  it  to  settle.  The 
clear  portion  is  then  used  for  the  test.  The  results  should  be 
expressed  as  parts  per  million  of  chlorine. 

Iron.  Iron  may  be  present  in  both  the  ferrous  and  ferric 
states.  In  ground  waters  it  is  usually  in  the  ferrous  condition 


366  WATER 

and  combined  with  carbonic  or  sulphuric  acid  or  with  organic 
matter.  After  exposure  to  air  it  is  frequently  present  as  a  col- 
loidal hydroxide.  Silt-bearing  waters  often  contain  much  iron 
in  suspension,  while  waters  contaminated  with  sewage  effluents 
and  manufacturing  wastes  contain  various  forms  of  iron  of 
different  degrees  of  solubility. 

The  total  iron  present  may  be  determined  as  follows:  Evapo- 
rate 100  c.c.  of  the  water  to  dryness  and  ignite  at  a  low  red 
heat.  After  cooling  add  5  c.c.  of  concentrated  hydrochloric 
acid,  moisten  the  surface  of  the  dish  and  warm  two  or  three 
minutes,  again  moisten  the  inner  surface  of  the  dish  with  the 
acid  and  wash  the  solution  into  a  5o-c.c.  Nessler  tube.  Dilute 
to  50  c.c.,  add  3  drops  of  N/5  potassium  permanganate  solution 
and  then  add  5  c.c.  of  potassium  sulphocyanide  solution.  Com- 
pare the  color  produced  with  that  from  solutions  of  known  iron 
content  similarly  treated  with  sulphocyanide. 

The  fixed  residue  from  a  previous  determination  may  be  dis- 
solved in  hydrochloric  acid,  converted  to  sulphates  by  evapora- 
tion with  sulphuric  acid,  and  treated  as  in  the  modified  Stokes 
and  Cain  method  as  applied  to  the  analysis  of  alum. 

Manganese.  The  determination  of  manganese  may  be  car- 
ried out  colorimetrically  if  the  water  contains  less  than  ten  parts 
per  million  but  if  more  than  this  amount  is  present  it  may  be 
preferable  to  use  a  volumetric  or  gravimetric  method. 

The  amount  of  water  used  should  contain  not  more  than  0.2 
mg.  of  manganese.  Add  to  it  2  c.c.  of  nitric  acid  (concentrated 
acid  diluted  with  an  equal  volume  of  water),  and  boil  down  to 
50  c.c.  Precipitate  the  chlorides  with  silver  nitrate,  being  sure 
that  a  slight  excess  is  used,  and  filter.  Add  about  0.5  gram 
ammonium  persulphate  crystals  and  warm  the  solution  until 
the  maximum  permanganate  color  is  developed,  which  usually 
takes  about  ten  minutes.  At  the  same  time  prepare  standards 
containing  0.2,  0.4,  0.6  c.c.,  etc.,  of  the  standard  manganous 
sulphate  solution  to  about  50  c.c.  and  treat  them  in  exactly 
the  same  way  as  the  standard.  Transfer  sample  and  standards 
to  Nessler  tubes  and  compare  the  color  at  once. 


MANGANESE  367 

The  standard  manganous  sulphate  is  prepared  by  dissolving 
0.288  gram  of  the  purest  potassium  permanganate  in  about 
100  c.c.  of  distilled  water,  acidifying  with  sulphuric  acid,  boiling 
and  just  discharging  the  color  with  a  dilute  solution  of  oxalic 
acid.  After  cooling  and  diluting  to  i  liter,  i  c.c.  of  the  solution 
contains  o.i  mg.  of  manganese. 


CHAPTER  XIV 
TESTING   WOOD   PULPS 

In  the  purchase  of  wood  pulp  it  is  very  desirable  to  have  some 
means  of  judging  its  quality,  as  otherwise  the  material  obtained  is 
quite  likely  to  be  entirely  unsuited  to  the  grade  of  paper  being 
made.  The  usual  crude  tests,  such  as  feeling  of  the  sheet,  tearing 
it  and  noting  the  length  of  fibre,  biting  the  fibre  to  note  its  hard- 
ness, etc.,  at  best  give  but  a  slight  idea  of  its  suitability  for  the 
work  in  question  and  if  intelligent  purchases  are .  to  be  made 
more  definite  methods  of  testing  must  be  devised.  Accurate 
sampling  and  testing  are  also  very  essential  in  the  case  of  moisture 
determinations,  since  pulp  is  purchased  on  a  10  per  cent  moisture 
basis  and  large  sums  of  money  are  frequently  at  stake. 

The  following  methods  are  those  which  have  been  gradually 
worked  out  during  years  of  experience  but  they  are  given  as  a 
working  basis  rather  than  as  final  and  unalterable  procedures, 
since  it  is  certain  that  many  of  them  are  capable  of  considerable 
improvement. 

Moisture  in  Wood  Pulp.  Baled  Pulp.  The  following  is  the 
official  method  of  sampling  and  testing  baled  pulp  as  adopted  by 
the  American  Paper  and  Pulp  Association  and  the  Association  of 
American  Wood  Pulp  Importers. 

"All  tests  must  be  made  by  a  chemist  duly  authorized  and 
approved  by  the  joint  committee  representing  the  Association  of 
American  Wood  Pulp  Importers  and  the  American  Pulp  and 
Paper  Association  on  one  side  and  the  Scandinavian  Wood  Pulp 
Associations  on  the  other  side,  and  must  be  made  strictly  in 
accordance  with  the  following  instructions  —  otherwise  the  com- 
mittee reserves  the  right  to  withdraw  the  approval  of  any 

chemist  at  any  time. 

368 


LOCATION  OF   BORINGS 


369 


"Before  proceeding  to  the  weighing  and  sampling  the  chemist 
must  ascertain  that  not  less  than  half  of  the  parcel  in  question  is 
available. 

"  Number.  Not  less  than  5  per  cent,  nor  more  than  10  per  cent 
of  the  entire  shipment,  but  not  less  than  ten  bales  shall  be  sam- 
pled. Samples  to  be  drawn  only  from  sound  and  intact  bales, 
from  different  sections  of  the  entire  shipment,  and  analyst  shall 
be  careful  to  observe  that  no  unusual  con- 
ditions prevail  in  the  selection  of  the  bales. 
The  accurate  weight  of  all  bales  sampled  to 
be  ascertained  by  sworn  weigher  before  samp- 
ling, or,  wherever  sworn  weigher  is  not  avail- 
able, by  a  competent  person  who  must  make 
sworn  affidavit  that  weights  are  correct,  and 
no  other  bales  than  those  weighed  to  be 
sampled,  and  whenever  bales  are  numbered, 
the  number  is  to  be  given  in  addition  to  the 
weight. 

"Method  of  Sampling 

"Depth  of  Boring.  The  sample  shall  be 
taken  by  boring  into  a  bale  to  a  depth  of  3  ins. 
(7.62  cm.)  with  a  special  auger  which  cuts 
a  disk  about  4  ins.  (10.16  cm.)  in  diameter. 

"Selection  of  Disks.  The  disks  shall  be 
removed,  and  ten  of  them  taken  as  a  sample, 
these  to  be  selected  as  follows: 

1  disk  2nd  sheet  from  the  wrapper. 

2  disks  i  in.  (2.5  cm.)  deep. 

3  disks  2  in.  (5.05  cm.)  deep. 

4  disks  3  in.  (7.62  cm.)  deep. 


FIG.  40.     CUTTER  FOR 
SAMPLING  PULP 


"  Location  of  Borings.  The  holes  to  be  bored  shall  be  so  located 
that  in  five  successive  bales  they  will  represent  a  portion  extend- 
ing diagonally  across  the  bale.  Each  bale  to  be  bored  but  once. 
The  first  hole  to  be  bored  at  the  corner,  the  edges  of  the  cut  being 


370  TESTING  WOOD  PULPS 

at  a  distance  of  one  inch  from  the  edge  of  the  bale.  The  second 
cut  shall  then  be  made  half  way  between  the  location  of  the  first 
cut  and  the  center  of  the  bale,  the  third  bale  shall  be  cut  at  the 
center,  the  fourth  bale  half  way  between  the  center  and  the  corner, 
and  the  fifth  bale  in  the  opposite  corner  in  a  position  correspond- 
ing to  the  first. 

"All  samples  must  be  either  weighed  immediately  after  being 
drawn  from  the  bales  by  accurate  scales,  or,  when  this  is  imprac- 
ticable, must  be  put  into  airtight  vessels,  made  of  metal  or  glass, 
with  ground-glass  or  metal  stoppers,  and  due  care  must  be  used 
in  the  transportation  of  such  samples  until  they  can  be  properly 
weighed  at  the  laboratory  of  the  chemists.  The  entire  bulk  of 
samples  selected  from  the  bales  must  be  dried  out  for  the  test. 
The  temperature  in  the  drying  oven  shall  not  exceed  212°  F. 

"Chemists  must  have  proper  and  adequate  equipment  for 
weighing  and  sampling  the  bales,  and  for  the  weighing  and 
drying  of  samples. 

"All  sampling  of  pulp  must  be  done  by  or  supervised  by  the 
approved  chemist  personally,  or  by  his  bona  fide  assistants  — 
each  chemist  to  file  with  the  committee  a  complete  list  of  his 
bona  fide  assistants  who  will  do  the  sampling,  such  list  to  have 
the  approval  of  the  committee.  The  chemist  will  be  held  respon- 
sible for  the  correct  sampling  by  his  approved  assistants.  The 
committee  shall  at  any  time  have  the  privilege  of  investigating 
the  sampling  done  by  chemists  or  their  assistants. 

"  Every  test  certificate  shall  clearly  state  the  name  of  the  person 
who  did  the  sampling. 

"The  test  certificates  hereafter  sjiall  be  uniform  and  in  accord- 
ance with  forms  to  be  approved  by  the  committee,  a  sample  draft 
of  which  will  be  furnished  by  the  committee  to  each  chemist." 

This  procedure  can  also  be  applied  to  rolls,  making  the  first 
boring  i  in.  from  the  end,  the  second  half  way  between  the  end 
and  the  middle,  the  third  at  the  middle,  and  so  on. 

This  method  of  testing  is  the  quickest  of  any  which  has  been 
proposed  and  it  leaves  the  bales  or  rolls  in  good  shape  to  be 
stored  or  shipped  but  it  is  not  necessarily  the  most  accurate.  In 


LAP  PULP  371 

the  opinion  of  the  author  it  favors  the  seller  of  the  pulp  since  the 
percentage  of  moisture  decreases  more  rapidly  on  the  outside 
than  in  the  centre  and  the  loss  in  the  weight  of  the  bale  does  not 
keep  pace  with  the  decrease  in  the  percentage  of  moisture  as 
shown  by  the  sample  taken.  This  is  particularly  true  of  bales 
put  aside  for  a  retest  and  stored  in  a  comparatively  dry  place  for 
several  weeks ;  such  retests  therefore  nearly  always  show  a  greater 
net  weight  of  air  dry  pulp  than  do  the  original  tests. 

The  quarter-sheet  method  of  sampling  consists  essentially  of 
opening  up  the  bales  and  taking  a  quarter  of  a  sheet  from  different 
parts  of  the  bale  in  such  a  way  that  the  combined  samples  would 
cover  the  entire  area  of  the  bale.  It  is  variously  applied  by  dif- 
ferent workers;  some  take  two  quarter-sheets  from  each  bale, 
others  more,  the  extreme  being  ten  quarter-sheets  starting  with 
the  second  sheet  from  the  wrapper  and  spacing  the  others  equally 
between  the  second  sheet  and  the  centre  of  the  bale.  On  the 
whole  it  is  believed  that  the  quarter-sheet  method  is  more  accu- 
rate than  the  disc  method  already  described  but  that  it  is  unprac- 
tical because  of  the  large  amount  of  time  and  labor  involved  and 
because  it  leaves  the  bales  in  no  condition  for  storage  or  further 
shipment. 

Lap  Pulp.  The  methods  of  testing  pulp  for  moisture  have 
been  exhaustively  investigated  by  the  Technical  Section  of  the 
Canadian  Pulp  and  Paper  Association.1  For  lap  pulp  from  ordi- 
nary wet  machines  or  Rogers  wet  machines  they  tentatively 
recommend  taking  a  strip  3  ins.  wide  clear  across  the  sheet  and 
to  the  full  thickness  of  the  sheet.  Such  a  sample  should  be 
taken  for  each  2000  Ibs.  of  wet  stock  in  the  shipment.  Tests 
by  this  method  in  comparison  with  the  entire  sheets  dried  out 
prove  that  the  two  methods  give  practically  identical  results  and 
that  the  strip  method  is  therefore  accurate. 

For  hydraulic  pressed  pulp  they  recommend  the  wedge  system 
as  proposed  by  Woodruff.2  They  have  proved  that  this  method 
gives  more  accurate  results  than  the  strip  method  in  which 

1  Slack:  Pulp  Paper  Mag.  Can.,  XVII,  1919,  265. 

2  Woodruff:  Paper,  Oct.  3,  1917,  p.  86. 


372  TESTING  WOOD  PULPS 

2-in.  strips  are  cut  from  the  centre  of  the  lap  to  the  outer  edge, 
the  cut  portions  forming  a  cross  for  each  four  samples.  In  the 
wedge  system  for  hydraulic  pulp  a  template  is  employed  to  mark 
the  laps.  This  template  has  an  angle  of  9  degs.  and  at  its  apex 
is  attached  a  disc  divided  into  forty  parts.  This  disc  is  placed  at 
the  centre  of  the  lap  and  the  wedge  marked  out  by  a  pencil  along 
the  edges  of  the  template.  The  lap  is  put  one  side  and  the  next 
marked  in  a  like  manner,  but  moving  the  wedge  of  the  template 
to  the  second  position  on  the  disc.  Forty  laps  are  thus  marked, 
giving  a  total  sample  equivalent  to  one  entire  lap.  The  marked 
laps  are  then  taken  to  a  circular  saw  and  the  wedges  cut  out. 
These  wedges  may  be  split  in  halves  if  it  is  necessary  to  reduce 
the  bulk  of  the  sample. 

Strength  or  Beating  Test.  This  method  of  testing  was  first 
described  by  the  writer  in  1915  l  and  was  the  outcome  of  an 
attempt  to  demonstrate  experimentally  the  variations  in  the 
strength  of  sheets  made  from  different  sulphite  fibres  after  they 
had  been  given  the  same  beating  treatment.  The  method  first 
proposed  is  as  follows: 

The  fibre  to  be  tested  is  allowed  to  become  air  dry  and  two  lots 
of  50  grams  each  are  then  weighed  out.  One  of  these  is  soaked  up 
in  1000  c.c.  of  water  and  reduced  to  pulp  by  rubbing  with  the 
hands;  it  is  then  rinsed  into  a  small  pebble  mill  with  just  1000 
c.c.  more  water.  The  mill  is  now  closed  and  allowed  to  revolve 
at  60  revolutions  per  minute  for  exactly  an  hour,  at  the  end 
of  which  time  the  entire  contents  are  emptied  upon  a  J-in.  mesh 
sieve  and  the  pulp  washed  off  the  stones  into  a  pan  placed 
beneath  the  sieve.  The  pan  is  then  filled  to  a  definite  mark  - 
27  liters  total  contents,  and  four  sheets  are  made  on  a  hand 
mould,  taking  two  dips  for  each  sheet  and  reversing  the  hand 
mould  between  dips  so  that  the  sheets  may  be  of  uniform  thick- 
ness on  the  two  edges.  After  pressing  between  felts  in  a  copying 
press  the  sheets  are  air  dried  and  are  then  tested  for  strength 
with  an  Ashcroft  tester.  Five  bursting  tests  are  made  on  each 
sheet  along  one  of  the  diagonals  and  the  average  of  the  twenty 

1  Paper,  Nov.  10,  1915. 


STRENGTH  OR  BEATING  TEST  373 

tests  taken  as  representing  the  beaten  strength  of  the  sample. 
If  it  is  desired  to  compare  the  strength  before  and  after  beating 
the  second  sample  of  50  grams  is  broken  up  into  a  pulp  as  before 
and  made  into  sheets  from  the  same  volume  of  water  as  in  the 
case  of  the  beaten  pulp. 

This  method  has  been  slightly  modified  1  by  the  Committee  on 
Sulphite  Pulp  of  the  Technical  Association  of  the  Pulp  and  Paper 
Industry  but  the  changes  they  propose  are  largely  to  shorten  the 
time  required  and  do  not  alter  any  of  the  essential  features  of  the 
test  as  originally  proposed. 

Many  factors  influence  the  results  of  this  test  and  in  order  to 
get  concordant  results  careful  control  is  necessary.  This  does  not 
lessen  the  value  of  the  method  but  it  means  that  intelligent  super- 
vision is  essential  if  the  best  information  is  to  be  derived.  Some 
of  the  vital  factors  will  be  briefly  mentioned. 

The  size  of  the  pebble  mill  as  well  as  its  volume  and  charge  of 
pebbles  must  be  carefully  considered.  Two  mills  of  the  same 
make  often  vary  enough  in  size  and  capacity  so  that  very  different 
beating  effects  are  obtained.  The  only  satisfactory  way  seems  to 
be  to  assume  one  to  be  right  and  adjust  the  charge  of  pebbles, 
fibre  and  water  in  the  other  so  that  the  same  strength  test  will 
be  given  by  the  beaten  fibre.  If  the  results  in  two  plants  are  to 
be  directly  comparable  it  will  of  course  be  necessary  to  stand- 
ardize their  pebble  mills  on  the  same  lots  of  fibre.  This  is  not  a 
serious  inconvenience  and  is  not  found  to  detract  much  from 
the  value  of  the  test  since  in  most  cases  comparative  results  only 
are  wanted. 

The  proportions  of  fibre  and  water  must  be  closely  adhered 
to,  as  comparatively  slight  variations  cause  appreciable  differ- 
ences in  the  bursting  strength.  This  is  also  true  of  the  time  of 
beating,  which  should  be  regulated  with  care  and  not  allowed  to 
vary  more  than  a  minute  or  two. 

Factors  having  minor  influence  on  the  tests  are  the  temperature 
of  the  water  in  the  pebble  mill  and  the  relative  humidity  of  the 

1  Paper,  Nov.  8,  1916. 


374  TESTING  WOOD  PULPS 

atmosphere  when  the  bursting  tests  are  made.     For  ordinary  rou- 
tine tests  consideration  of  these  factors  may  be  neglected. 

A  variable  having  great  influence  in  many  cases  is  that  of  the 
moisture  in  the  pulp  when  taken  for  the  test.  Wet  pulp  will 
not  give  the  same  test  as  it  will  after  being  air  dried.  Experi- 
ments on  one  lot  of  pulp  showed  that  the  beaten  strength  was 
highest  in  the  wet  lap  and  decreased  as  the  moisture  diminished; 
the  change  from  70  to  5  per  cent  moisture  reduced  the  bursting 
strength  from  64.7  Ibs.  to  40  Ibs.  This  change  cannot  be  reversed 
by  wetting  dry  pulp,  which  indicates  the  reason  for  air  drying  all 
samples  before  testing  so  that  all  may  be  on  the  same  basis.  For 
the  most  accurate  work  it  would  be  very  desirable  to  dry  all 
samples  at  a  constant  humidity  since  this  would  insure  more 
concordant  results.  One  of  the  changes  which  it  was  proposed 
to  make  in  the  original  method  was  to  press  the  samples  of  wet 
pulp  to  a  constant  moisture  and  use  this  pulp  as  a  basis  for  the 
test.  This  shortens  the  time  required  but  it  does  not  permit  com- 
parison of  the  wet  pulp  with  one  received  in  the  air  dry  condition. 

A  point  of  very  great  importance  is  the  manner  of  forming  the 
sheets  to  be  tested.  If  a  hand  mould  is  used  the  weight  of  the 
sheets  varies  considerably  depending  on  whether  the  fibre  is 
"free"  or  " greasy"  after  beating.  It  has  been  proposed  to  get 
around  this  difficulty  by  calculating  the  breaking  test  per  unit 
weight  of  sheet  but  this  is  not  an  entirely  satisfactory  method. 
All  such  variations  can  be  eliminated  by  using  some  form  of  sheet 
making  machine  in  which  a  constant  volume  of  stock  is  used 
and  none  is  lost  by  overflowing  the  edges  as  happens  with  the 
deckle  of  the  hand  mould. 

Different  methods  of  employing  this  test  may  be  used;  the  j 
original  idea  was  to  beat  for  a  fixed  time  and  note  the  differences 
in  the  strength  developed,  but  Hatch  1  has  adopted  the  modifica- 
tion of  beating  a  number  of  samples  for  different  lengths  of  time 
in  order  to  see  what  maximum  strength  would  be  developed  and 
the  time  necessary  for  its  production. 

For  other  interesting  data  relating  to  the  beating  test  reference 

1  Paper,  Oct.  3,  1917. 


COLOR   COMPARISON  OF  BLEACHED   PULPS  375 

is  made  to  the  work  of  Mansfield  and  Stephenson l  and  of 
Sutermeister.2 

This  method  of  testing  gives  satisfactory  results  with  sulphite, 
soda,  and  sulphate  pulps  but  does  not  appear  suitable  for  ground 
wood  since  the  latter  is  not  affected  by  the  beating  treatment  to 
nearly  so  great  an  extent  as  the  others. 

Color  Comparison  of  Bleached  Pulps.  The  method  outlined 
here  has  been  taken,  with  slight  modifications,  from  the  report 
of  the  Committee  on  Sulphite  Pulp  of  the  Technical  Association 
of  the  Pulp  and  Paper  Industry.3 

The  grading  of  the  shade  of  a  piece  of  bleached  pulp  usually 
leads  to  very  uncertain  results.  Two  pieces  of  pulp,  which  under 
certain  conditions  of  light  appear  identical  in  shade,  under 
different  light  conditions  appear  to  be  very  different  in  shade. 
Very  often  bleached  pulp  which  is  satisfactory  in  shade  under 
artificial  light,  appears  quite  yellow  in  daylight.  Again,  different 
pieces  of  the  same  pulp  often  appear  to  be  of  different  shade, 
when  graded  together  under  identical  light  conditions.  This 
latter  phenomenon  can  be  due  only  to  one  cause:  differences  in 
the  surfaces  of  the  two  pieces  of  the  same  pulp.  The  problem 
to  be  solved  therefore  appeared  to  be  twofold. 

1.  To  devise  some  means  of  obtaining  constant  illumination 
conditions;    and  this  illumination  to  be  of  such  a  quality  that 
slight  differences  in  shade  could  be  easily  distinguished. 

2.  To  devise  a  means  whereby 

(a)  the  surface   of  different  pulps  could  be  made  the 

same,  or 
(&)  the  effects   of  different   surfaces  of  different  pulps 

could  be  minimized. 

Many  so  called  daylight  lamps  were  tried,  including  both  the 
bulb  and  arc  types.  Finally  the  arc  type  of  color  comparator 
made  by  the  General  Electric  Company  was  adopted  as  giving 

1  Pulp  Paper  Mag.  Can.,  Oct.  i,  1916. 

2  Paper,  Dec.  n,  1918. 

3  Paper,  Nov.  8,  1916,  19,  No.  9. 


TESTING  WOOD  PULPS 

the  most  constant  artificial  light  of  all  those  tried  out  and  a 
light  whereby  one  could  most  easily  distinguish  small  differences 
of  shade. 

The  procedure  adopted  consists  in  attaching  six  disks  of  the 
pulp  to  be  tested  to  the  front  of  six  wheels  of  varying  degrees  of 
whiteness.  The  wheels  and  pulp  are  then  revolved  at  high  speed 
(2,500  revolutions  per  minute)  and  the  operator  judges  to  which 
of  the  standardized  color  wheels  the  pulp  is  nearest  in  shade. 
The  shade  of  pulp  is  then  declared  to  be  that  of  the  wheel  to  which 
it  is  nearest  in  color.  The  test  being  made  always  under  the 
same  conditions  of  illumination  both  variable  factors  of  light  and 
pulp  surface  are  rendered  constant  and  thereby  the  remaining 
variable,  the  actual  shade  of  pulp,  can  be  easily  determined. 

Description  of  Apparatus 

1.  Cutting  Press.     The  disks  of  pulp  are  cut  with  a  press  and 
dies  of  the  type  FO2,  made  by  the  Ferracute  Machine  Company, 
of  Bridgeton,  N.  J.     The  dies  are  so  arranged  that  a  disk  3^  ins. 
in  diameter  is  cut  with  a  f  in.  hole  in  the  center,  at  one  operation. 

2.  Revolving  Disk  Machine.     Fig.  41  gives  details  of  the  con- 
struction of  this  apparatus.     The  method  of  preparing  the  differ- 
ently shaded  wheels  is  as  follows:   Different   combinations  of 
plaster  of  Paris,  magnesia  and  chromate  of  potash  are  made  into 
a  paste  with  water,  this  paste  poured  into  the  brass  wheel,  allowed 
to  set  and  then  planed  down  to  a  smooth  surface. 

It  is  recognized,  of  course,  that  one  fixed  standard  of  color 
shade  is  not  applicable  as  a  standard  to  all  kinds  of  pulp.  For 
example:  bleached  pulp  when  run  from  a  drying  machine  has  a 
radically  different  shade  from  the  same  pulp  run  through  a  wet 
machine  and  hydraulically  pressed.  Yet  both  pulps  on  being 
made  into  paper  would  give  identical  color  shades  to  the  paper. 
Hence,  it  is  necessary  to  employ  different  color  mixtures  on  the 
revolving  disk  machine  for  different  types  of  pulp.  Again  the 
standard  of  pulp  color  shade  demanded  by  some  manufacturers 
of  paper  is  entirely  different  from  that  of  other  manufacturers. 
Hence  it  is  not  possible  to  recommend  a  formula  applicable  to 


(377) 


X378) 


DAYLIGHT  LAMPS 


379 


all  cases.  The  formula  given  here  is  applicable  to  bleached 
drier  pulp  and  the  color  95,  as  named  in  this  report,  when  applied 
to  this  product  is  satisfactory  to  the  great  majority  of  paper 
manufacturers  in  this  country. 

The  different  wheels  are  numbered  as  follows,  reading  from 
left  to  right: 

ico,  95,  90,  85,  80,  75. 

The  formulas  are  as  follows: 


No.  of  wheel 

Water 

Plaster  of 
Paris 

Chromate  of 
potash 

Magnesia, 
powdered 

100 

120 

107 

O.O 

2O 

95 

120 

107 

0.0245 

2O 

90 
85 
80 

1  20 

120 

1  20 

214 
214 
214 

0  .  1490 
0.4660 
0.6120 

O 
0 
0 

75 

1  20 

214 

0.7770 

O 

The  plaster  of  Paris  and  magnesia  are  first  thoroughly  mixed 
together,  then  the  water  added  and  the  paste  thoroughly  stirred 
up  and  poured  into  the  wheel. 

When  pouring  the  wheels  containing  the  chromate,  the  latter 
is  first  dissolved  in  the  water,  the  solution  added  to  the  plaster  of 
Paris,  the  whole  thoroughly  stirred  up  and  poured  into  the  wheel. 

After  pouring,  the  wheels  are  allowed  to  set  forty-eight  hours 
and  then  revolved  by  means  of  the  motor,  and  turned  down 
smooth  with  a  sharp-edged  cold  chisel  and  finished  with  fine 
sandpaper. 

A  sewing  machine  belt  was  tried  out  to  drive  the  machine,  but 
a  satisfactory  fastener  could  not  be  found  which  at  the  speed 
employed  would  not  pull  out  after  a  short  time.  It  was  found 
that  J  in.  rope  with  a  spliced  joint  stands  up  very  well. 

3.  Daylight  Lamps.  Two  of  these,  manufactured  by  the 
General  Electric  Company,  are  used.  They  are  known  as  their 
direct  current  multiple  color  matching  outfits.  The  whole 
apparatus,  of  course,  is  placed  in  a  dark  room,  where  no  light 
rays  can  penetrate  to  interfere  with  the  light  of  the  lamps. 


380  TESTING  WOOD  PULPS 

This  method  of  testing  is  a  noteworthy  attempt  at  putting 
the  designation  of  color  on  a  numerical  basis  in  a  practical  way 
and  it  is  in  successful  operation  in  several  mills.  The  equipment 
is  however  rather  expensive,  and  if  several  grades  of  pulp,  such 
as  soda  poplar,  sulphite  spruce,  and  sulphate  pine,  are  to  be 
examined  a  large  number  of  standard  discs  must  be  kept  on 
hand  and  the  preparation  of  the  filling  for  such  discs  is  by  no 
means  easy  and  is  often  quite  unsatisfactory. 

It  is  the  belief  of  the  author  that  fully  as  reliable  comparisons 
can  be  made  by  using  hand  mould  sheets  as  explained  under 
"Bleaching  Qualities."  It  is  of  course  desirable  that  such  com- 
parisons should  be  made  under  a  "  day  light  lamp"  in  a  dark 
room  but  if  this  is  not  available  a  north  light  should  be  used  and 
tests  made  at  as  nearly  as  possible  the  same  time  each  day. 

Bleaching  Qualities.  The  method  used  in  determining  the 
bleach  required  by  a  sample  of  fibre  depends  on  the  point  of 
view  of  the  observer  and  should  in  general  be  made  to  conform  as 
closely  as  possible  to  actual  operations  in  the  plant  in  question. 
The  method  preferred  by  the  author  is  as  follows :  Two  5o-gram 
samples  of  the  fibre  are  weighed  out  and  at  the  same  time  a  small 
sample  is  taken  for  a  moisture  test.  From  this  moisture  test 
it  is  possible  to  calculate  the  air  dry  fibre  (10  per  cent  moisture) 
corresponding  to  the  5o-gram  samples  and  upon  this  air  dry 
weight  the  figures  for  bleach  are  based.  One  of  the  samples  is 
now  broken  up  in  a  little  water  in  a  6-in.  by  8-in.  battery  jar  until 
a  uniform  pulp  is  obtained  and  this  is  then  diluted  to  about  two 
liters  with  water.  From  a  solution  of  bleaching  powder,  whose 
strength  has  previously  been  determined,  a  volume  is  measured 
out  which  corresponds  to  the  percentage  of  bleach  which  it  is 
estimated  the  fibre  will  require.  This  is  added  to  the  jar  of  pulp 
and  the  contents  kept  agitated  and  at  about  35°  to  40°  C.  until 
the  bleach  is  just  exhausted.  The  fibre  is  then  thrown  upon 
a  screen  of  yo-mesh  wire  and  washed  with  a  heavy  stream  of 
water  to  remove  the  bleach  residues  and  break  up  any  knots  or 
balls  of  fibre  which  may  have  formed.  The  pulp  is  next  made 
into  hand  mould  sheets  which  are  dried  on  a  small  steam  heated 


BLEACHING  QUALITIES  381 

cylinder  and  compared  with  sheets  of  pulp  of  the  standard  color. 
If  the  color  is  found  to  be  much  different  from  the  standard  a 
second  test  is  made  using  more  or  less  bleach  as  the  first  test 
indicates. 

Since  bleached  fibre  slowly  changes  in  color  it  is  quite  essential 
to  obtain  some  permanent  standard  but  so  far  efforts  along  this 
line  have  not  been  entirely  successful.  Plates  of  dull  porcelain 
have  been  suggested  but  the  difference  in  surface  texture  between 
the  porcelain  and  the  fibre  sheets  would  probably  render  the 
comparison  of  their  colors  quite  unsatisfactory.  Attempts  have 
also  been  made  to  use  slabs  of  plaster  of  Paris  tinted  to  the  right 
shade  and  given  the  desired  surface  texture  by  pressing  between 
felts.  Great  difficulty  was  experienced  in  getting  just  the  right 
color  in  such  slabs.  The  most  practical  method  seems  to  be  to 
cut  out  a  large  number  of  samples  from  the  same  lot  of  unbleached 
pulp  and  determine  with  great  care  the  amount  of  bleach  required 
to  give  the  standard  white  color.  After  this  is  determined  one 
sample  is  bleached  each  month,  the  sheets  made  therefrom  serv- 
ing as  the  standard  for  the  month  following. 

In  plants  where  practically  this  same  method  of  bleaching  is 
carried  out  the  above  scheme  of  testing  is  found  to  give  results 
in  very  close  agreement  with  those  of  actual  practice.  In  other 
plants  where  an  excess  of  bleach  is  added  and  the  residual  bleach 
washed  out  after  the  color  is  brought  up  to  the  desired  shade  a 
method  of  testing  employing  these  same  principles  should  be 
used.  In  such  tests  a  known  amount  of  bleach  is  added  and 
that  remaining  at  the  end  of  the  test  is  determined  by  analysis; 
from  these  data  the  per  cent  used  by  the  fibre  may  be  calculated. 
This  method  of  testing  is  quicker  than  the  one  first  given  but  it 
is  necessary  to  compare  the  colors  of  the  bleached  fibres  in  the 
wet  state  before  the  yellow  products  of  the  bleaching  action  have 
been  removed. 

Richter  1  has  suggested  a  method  of  testing  sulphite  fibres 
which  depends  on  the  comparison  of  the  colors  developed  on  treat- 
ing samples  of  unbleached  fibre  with  nitric  acid.  Weighed  sam- 

1  E.  Richter:  Proc.  Eighth  Int.  Cong.  Appd.  Chem. 


382  TESTING  WOOD  PULPS 

pies  of  the  fibre  to  be  tested,  and  also  of  one  whose  bleaching 
properties  are  known,  are  treated  with  13  per  cent  nitric  acid 
solution  for  about  an  hour;  portions  of  the  acid  are  then  drawn 
off  and  compared  in  a  colorimeter  of  any  standard  construction. 
Knowing  the  bleach  required  by  one  fibre  it  is  possible  to  esti- 
mate that  necessary  to  produce  the  same  color  in  the  other 
sample.  This  method  is  quick  and  may  possibly  be  reasonably 
accurate  with  fibres  cooked  under  nearly  the  same  conditions  but 
with  samples  from  a  number  of  different  mills  it  proved  to  be 
only  approximate,  some  of  the  results  being  as  much  as  10  to  15 
per  cent  higher  or  lower  than  the  figures  obtained  by  actual  bleach- 
ing trials.  Moreover  it  does  not  appear  to  be  applicable  to 
soda  and  sulphate  fibres,  at  least  when  a  sulphite  fibre  is  used  as 
a  standard  for  comparison. 

Loss  in  Weight  on  Bleaching.  This  test,  taken  in  connection 
with  the  bleaching  test,  throws  considerable  light  on  the  value  of 
a  pulp,  since  it  shows  what  loss  in  weight  will  be  suffered  by  the 
fibre  because  of  the  oxidizing  and  solvent  action  of  the  bleach, 
apart  from  the  mechanical  loss  in  the  bleaching  process,  which 
should  be  practically  the  same  for  all  fibres.  The  method  is  as 
follows: 

Weigh  out  two  samples  of  about  2  grams  each  and  determine 
the  moisture  in  one  by  drying  to  constant  weight  at  100°  to  105°. 
The  second  sample  is  broken  up  to  a  pulp  in  a  little  water  by 
rubbing  between  the  thumb  and  fingers  and  the  pulp  transferred 
to  a  small  flask.  This  procedure  requires  care  and  skill  but  after 
a  little  experience  it  can  be  done  with  no  loss  of  fibre.  Bleach 
solution  is  now  added  from  a  burette,  the  amount  being  regulated 
to  give  the  percentage  which  the  bleaching  test  proved  would 
give  the  standard  white  color  in  the  sample  being  tested.  The 
flask  is  now  kept  at  about  35°  to  40°  until  the  bleach  is  exhausted, 
when  the  fibre  is  transferred  to  a  Gooch  crucible,  washed  very 
thoroughly  with  hot  water,  dried  and  weighed.  The  difference 
in  the  bone  dry  weight  of  the  unbleached  and  bleached  fibre, 
which  shows  the  loss  due  to  the  chemical  action  of  the  bleach, 
may  conveniently  be  expressed  as  percentage  of  the  former. 


NATURE  AND  AMOUNT  OF  DIRT  383 

Sedimentation  Test.  This  test  is  one  which  has  not  yet  been 
standardized  but  which  has  been  applied  to  the  study  of  pulps 
by  many  different  observers  most  of  whom  used  home-made  ap- 
paratus of  some  sort.  The  principle  of  the  test  is  that  the  longer 
the  fibres  have  been  beaten,  or  in  the  case  of  ground  wood 
the  finer  it  is  ground,  the  more  slowly  it  will  part  with  its  water. 
The  general  method  of  making  the  test  is  to  place  a  known 
amount  of  fibre,  reduced  to  a  uniform  pulp  in  a  definite  volume 
of  water,  in  some  sort  of  receptacle  with  a  perforated  bottom 
through  which  the  water  can  drain  and  on  which  the  fibre  settles 
to  form  a  mat.  A  valve  below  the  false  bottom  prevents  the 
escape  of  the  water  until  the  desired  time  and  makes  it  possible 
to  record  the  time  of  outflow.  In  Fishburn  and  Weber's  appara- 
tus 1  the  receptacle  is  a  graduated  glass  cylinder  and  the  test 
consists  in  noting  the  time  required  for  the  water  level  to  drop 
gi  ins.  In  the  Riegler-Schopper2  tester,  Fig.  42,  the  water  drain- 
ing from  the  stock  falls  into  a  chamber  having  two  discharge  out- 
lets of  different  dimensions  and  at  different  levels.  The  amount 
of  water  issuing  from  the  large  orifice,  which  is  at  the  higher 
level,  gives  an  indication  of  the  degree  of  beating  or  the  natural 
slowness  or  quickness  of  the  stock.  The  smaller  opening,  which 
discharges  under  a  practically  constant  head,  acts  as  a  sort  of 
automatic  cut-off  and  by  taking  care  of  the  last  slow  drainage 
from  the  test  sample  it  makes  the  differences  in  the  results  more 
marked. 

A  test  of  this  nature,  using  a  long  tube  as  a  sedimentation 
chamber,  has  been  used  in  testing  sulphite  pulps  and  it  is 
claimed3  that  it  shows  very  marked  differences  between  long 
and  short  fibred  stocks. 

Nature  and  Amount  of  Dirt.  The  dirt  in  a  sample  of  pulp 
can  be  successfully  investigated  if  a  sheet  of  it  is  wet  and  examined 
by  transmitted  light.  A  convenient  outfit  consists  of  a  box 
painted  white  inside  and  fitted  with  two  or  more  electric  light 

1  Fishburn  and  Weber:  Paper,  Oct.  n,  1916,  13. 

2  U.  S.  Pat.  1,193,613,  Aug.  8,  1916.     Paper,  Aug.  30,  1916. 

3  "Snowshoe":  Pulp  Paper  Mag.  Can.,  Sept.  5,  1918,  XVI,  793. 


384 


TESTING  WOOD  PULPS 


NATURE  AND  AMOUNT  OF  DIRT  385 

bulbs.  The  top  of  the  box  consists  of  a  glass  plate  upon  which 
the  pulp  rests.  This  box  may  be  of  any  convenient  size  but  the 
sample  of  pulp  should  completely  cover  its  top  so  that  no  glare 
from  the  lights  enters  the  observer's  eyes.  If  a  box  is  made  to 
take  a  sheet  6J  X  8  ins.  and  the  dirt  is  counted  on  both  sides  a 
simple  multiplication  by  2  gives  the  dirt  count  per  100  sq.  ins., 
which  has  been  found  a  satisfactory  method  of  expressing  the 
results.  The  sheets  to  be  examined  should  be  of  nearly  uniform 
thickness  so  that  the  count  may  be  on  practically  the  same 
quantity  of  pulp  in  every  case.  If  desired  the  dry  sheets  can  be 
weighed  before  testing  and  in  this  way  the  dirt  count  can  be  placed 
on  a  weight  basis.  If  the  material  in  question  is  not  received 
in  the  form  of  sheets  it  may  be  made  into  sheets  on  a  hand  mould 
before  examination.  It  will  be  found  convenient  to  dry  these 
completely  and  again  wet  them  before  examination;  this  will 
enable  the  wet  sheets  to  be  handled  with  much  less  trouble  than 
if  they  are  taken  direct  from  the  hand  mould  in  which  case  they 
tear  so  readily  that  they  are  extremely  difficult  to  turn  over.  In 
making  this  test  it  is  well  to  dig  out  with  a  needle  the  specks  of 
dirt  which  are  not  directly  on  the  surface,  since  particles  which 
appear  to  be  dirt,  will,  in  some  cases,  prove  to  be  small  rolls  of 
fibre.  It  is  also  desirable  to  record  the  results  under  at  least 
two  headings,  dirt  and  shives,  and  in  some  special  cases  it  is  even 
well  to  classify  them  in  such  groups  as  cinders,  bark,  iron  rust, 
etc.,  as  this  will  often  enable  the  chief  cause  of  the  trouble  to  be 
located. 

The  results  obtained  in  this  test  depend  almost  entirely  on  the 
opinion  of  the  observer  as  to  what  constitutes  dirt  and  since  the 
opinion  of  different  observers  often  varies  widely  it  is  plain  that 
the  tests  should  all  be  made  by  one  person  in  order  to  avoid  the 
personal  factor.  Records  of  this  nature  are  valuable  in  showing 
whether  the  product  of  any  plant  is  being  kept  up  to  standard  and 
they  are  also  helpful  in  selecting  pulps  in  the  market  when 
purchases  are  in  question. 


CHAPTER  XV 
PAPER  TESTING 

In  the  following  chapter  are  given  the  methods  in  common 
use  in  the  testing  of  paper,  together  with  some  of  the  more 
unusual  tests  which  are  occasionally  called  for.  It  has  been 
attempted  to  give  these  methods  concisely  but  in  sufficient 
detail  to  enable  them  to  be  carried  out  without  difficulty  by 
any  technically-trained  man  who  has  had  some  experience  in 
the  paper  industry.  It  should  not  be  forgotten,  however,  that 
the  intelligent  interpretation  of  the  results  depends  in  many 
cases  upon  the  judgment  of  the  observer  and  that  good  judg- 
ment can  only  be  replaced  to  a  slight  extent  by  even  the  most 
detailed  directions. 

The  essential  features  of  a  number  of  these  tests  have  been 
taken  from  the  report  of  the  Committee  on  Paper  Testing  of  the 
Technical  Association,1  to  which  acknowledgement  is  hereby 
made,  and  the  student  is  referred  to  this  report  for  more  com- 
plete details  of  many  of  the  methods.  There  are  also  included 
a  considerable  number  of  tests  which  are  not  mentioned  in  this 
report  but  which  practical  experience  has  shown  to  be  of  value 
in  the  study  of  paper.  For  a  more  detailed  study  of  the  factors 
influencing  many  of  these  tests  reference  should  also  be  made 
to  Herzberg's  "Papierprufung,"  2  where  the  subject  is  exhaust- 
ively treated.  The  methods  of  testing  are  grouped  under  three 
heads:  microscopical  examinations,  physical  testing,  and  chemi- 
cal analysis. 

Microscopical  Examinations 

The  microscope  offers  practically  the  only  means  for  deter- 
mining the  kinds  of  fibres  and  the  relative  proportions  of  each 

1  Paper  XXV,  693,  739,  777,  831  and  877,  Dec.  10,  17,  24,  31,  1919,  Jan.  7,  1920. 

2  Herzberg:  Papierprufung,  Berlin,  1907. 

386 


ESTIMATION  OF  FIBRE  CONTENT  387 

in  a  sample  of  paper  and  it  is  therefore  the  universal  method 
for  making  a  fibre  analysis.  The  method  is  rapid,  and  in  the 
hands  of  an  expert  is  fairly  accurate,  but  it  is  probably  not 
desirable  to  attempt  to  estimate  percentages  much  closer  than 
5  per  cent.  The  accuracy  attainable  depends  upon  two  factors 
(i)  the  kind  of  mixture  under  examination,  i.e.,  whether  two  or 
more  fibres,  and  how  beaten  and  (2)  the  experience  and  care  of 
the  observer.  As  a  rule,  the  opinion  of  one  thoroughly  trained 
and  careful  analyst  is  more  exact  than  the  average  judgment  of 
several  inexpert  men  who  have  spent  collectively  much  more 
time  on  the  examination. 

The  microscope  used  should  be  of  some  standard  make  go  that 
attachments  may  be  added  from  time  to  time  as  seems  desir- 
able. The  particular  kind  of  microscope  and  whether  monocu- 
lar or  binocular  is  largely  a  matter  of  personal  preference.  This 
also  holds  true  of  the  magnification  employed,  some  advocating 
45  diameters  and  others  120  or  even  as  high  as  160  diameters. 
An  instrument  with  two- thirds  and  one-sixth  inch  objectives 
and  i-  and  2-inch  eyepieces  will  be  found  to  give  as  great  a 
range  of  magnification  as  is  necessary  for  all  ordinary  paper- 
mill  work.  A  substage  condenser  and  iris  diaphragm  should 
by  all  means  be  included  and  it  is  very  desirable  to  add  a  stage 
micrometer  and  an  eyepiece  micrometer. 

Estimation  of  Fibre  Content.  In  order  that  the  sample  taken 
shall  be  representative  several  small  pieces  should  be  clipped 
from  various  parts  of  the  sheet,  or  if  several  sheets  are  available 
small  pieces  should  be  taken  from  each.  These  should  be  placed 
in  a  dish,  small  flask,  or  any  suitable  container,  covered  with 
0.5  per  cent  caustic  soda  solution,  and  heated  to  the  boiling 
point  in  order  to  dissolve  sizing  or  binding  materials.  The 
samples  are  then  washed  several  times  in  water,  rolled  into  a 
ball  and  kneaded  between  the  thumb  and  finger  and  then  re- 
duced to  a  pulp  by  shaking  vigorously  in  a  test  tube  about 
half  full  of  water,  t/k  small  sample  is  then  removed  from  the 
test  tube  by  means  of  a  needle,  placed  on  a  microscope  slide 
and  the  water  removed  by  touching  the  drop  with  a  piece  of 


388  PAPER  TESTING 

folded  filter  paper  of  ordinary  quality.  The  fibres  are  covered 
with  a  drop  or  two  of  Herzberg's  stain,  carefully  separated  by 
the  aid  of  microscope  needles,  so  that  they  will  not  lie  too  much 
in  a  bunch,  and  they  are  then  covered  with  a  cover  glass.  The 
slide  is  then  ready  for  examination  by  means  of  the  microscope. 

In  preparing  the  sample  for  examination  a  number  of  pre- 
cautions must  be  observed  if  good  results  are  to  be  obtained, 
and  a  discussion  of  some  of  these  important  points  will  be  help- 
ful, at  least  to  those  who  are  just  beginning  the  work. 

There  are  several  methods  of  removing  a  representative 
sample  from  the  test  tube.  Spence  and  Krauss 1  prepare  a 
rather  dilute  pulp  in  a  test  tube  about  f  X  8  ins.  and  for  re- 
moving the  sample  use  a  glass  tube  10  ins.  long  by  A-in.  in 
diameter.  This  tube  is  fitted  with  a  small  rubber  bulb  at  one 
end  while  the  walls  at  the  other  are  rounded  to  present  a  smooth 
surface.  The  test  tube  is  well  shaken,  the  dropper  quickly 
inserted  2  ins.  below  the  surface,  two  bubbles  of  air  expelled 
and  about  half  an  inch  of  mixture  drawn  into  the  tube.  This 
entire  portion  is 'transferred  to  slides,  making  four  drops  in  all, 
and  the  water  removed  by  evaporation  in  an  air  bath.  The 
slides  are  then  ready  to  stain  and  examine. 

Another  and  more  usual  method  is  to  prepare  the  mixture  in 
a  smaller  test  tube,  say  f  X  6  ins.,  and  after  shaking  vigorously 
remove  the  sample  by  inserting  a  microscope  needle  and  taking 
out  a  small  bunch  of  the  fibres.  This  method  is  better  for 
long-fibred  stock  such  as  bond,  ledger  and  writing  papers,  while 
the  first  method  is  safer  for  ground-wood  papers  and  others 
where  very  short  fibres  are  present. 

A  modified  form  of  the  second  method,  which  makes  it  appli- 
cable to  all  grades  of  paper,  is  to  prepare  the  mixture  of  such 
density  that  on  shaking  the  test  tube  and  then  placing  it  up- 
right, small  clots  of  fibre  will  remain  adhering  to  the  walls  of 
the  tube  above  the  liquid.  The  sample  is  then  obtained  by 
removing  all  the  fibre  included  in  one  of  these  small  clots. 

Removal  of  water  from  the  sample  before  staining  may  be 

1  Spence  and  Krauss:  Paper,  20,  1917,  p.  12,  May  23. 


ESTIMATION  OF  FIBRE   CONTENT  389 

done  with  filter  paper  or  by  drying  as  already  outlined,  or  a 
blotting  paper  of  firm  texture  may  be  pressed  down  directly 
on  the  drop  on  the  slide.  This  removes  the  water  and  leaves 
the  fibre  adhering  to  the  slide  ready  for  staining.  If  a  firm 
blotter,  free  from  lint,  is  used  and  any  loose  fibres  are  removed 
by  blowing  upon  its  surface  just  before  applying  it,  no  contami- 
nation of  the  sample  need  be  feared.  Another  method  is  to  place 
the  sample  removed  by  the  needle  from  the  test  tube  directly 
upon  a  piece  of  suitable  filter  or  absorbent  paper;  this  takes  up 
the  water  and  the  fibre  can  then  be  transferred  to  the  slide. 

The  use  of  very  thin  cover  glasses  for  covering  the  stained 
specimen  is  only  to  be  recommended  when  very  high  magnifi- 
cation is  to  be  used.  In  nearly  all  fibre  analysis  it  is  quite 
sufficient  to  use  a  second  thin  microscope  slide  as  a  cover.  This 
permits  several  fields  to  be  prepared  on  one  slide  and  eliminates 
much  breakage.  The  slide  as  a  cover  glass  also  possesses  an- 
other advantage  over  the  lighter  and  thinner  form:  if  the  sample 
is  well  loosened  up  with  the  needle  so  that  no  lumps  remain 
and  the  slide  is  then  dropped  onto  it  from  a  distance  of  half  an 
inch  or  so  a  very  even  distribution  of  the  fibres  can  be  obtained. 

The  Herzberg  stain,  which  is  very  generally  used,  is  made  up 
according  to  the  following  formula: 

Solution  A.     20  grams  zinc  chloride  dissolved  in  10  c.c.  of   | 
distilled  water.  V 

Solution  B.  2.1  grams  potassium  iodide  and  o.i  gram  iodine 
dissolved  in  5  c.c.  of  distilled  water. 

Prepare  the  two  solutions  separately,  mix  and  allow  the  mix- 
ture to  stand  several  hours  or  until  all  sediment  has  settled  out. 
The  clear  liquid  is  then  decanted  and  is  ready  for  use  in  staining 
fibres;  it  should  be  kept  in  a  brown  glass  bottle  or  else  in  the 
dark.  This  stain  gives  different  colors  with  different  kinds  of 
fibres;  ground  wood,  jute,  flax  tow,  uncooked  manila  hemp  and 
practically  all  highly  lignified  tissues  are  colored  yellow  or  lemon 
yellow.  Thoroughly  cooked  and  bleached  soda  and  sulphite 
pulps  as  well  as  bleached  straw  and  esparto  fibres  are  colored 


390  PAPER   TESTING 

blue  or  navy  blue.  Cotton  and  linen  rags,  thoroughly  cooked 
and  bleached  manila  hemp  and  some  of  the  Japanese  fibres  are 
colored  wine  red. 

It  is  very  essential  that  this  stain  be  so  made  up  as  to  give 
satisfactory  colors  on  the  different  fibres.  Its  quality  should 
be  proved  by  staining  a  mixture  of  fibres  known  to  contain 
about  equal  proportions  of  rag,  bleached  sulphite  and  bleached 
soda  fibres.  If  the  stain  is  satisfactory,  the  soda  pulp  should 
stain  a  dark  blue  color,  while  the  sulphite,  because  of  its  thinner 
walls,  will  be  a  light  blue,  and  the  rag  fibres  will  be  red  or  wine- 
red.  If  the  blue  is  not  clear  but  tends  toward  the  violet,  too 
much  iodine  is  present  and  more  water  or  zinc  chloride  should 
be  added.  A  stain  which  gives  the  best  results  with  ground 
wood  will  not  always  be  entirely  satisfactory  with  mixtures  of 
well-bleached  fibres  and  if  widely  varying  papers  are  to  be 
examined,  it  is  well  to  keep  on  hand  a  number  of  stains  so  ad- 
justed that  one  suitable  for  any  grade  of  fibre  is  available.  One 
should  be  prepared  to  give  a  bright  lemon  yellow  on  ground 
wood;  a  second  should  give  the  colors  already  mentioned  on 
sulphite,  soda  and  rag  fibres,  etc. 

A  stain  which  is  considered  by  some  to  be  better  than  the 
Herzberg  stain  is  made  up  as  follows: 

Solution  A.  1.3  grams  iodirie  and  1.8  grams  potassium  iodide 
in  100  c.c.  of  water. 

Solution  B.  A  clear,  practically  saturated  solution  of  calcium 
chloride. 

In  using  this  stain  apply  a  drop  or  two  of  solution  A  to  the 
moist  fibres  on  the  microscope  slide.  After  a  minute  or  so  re- 
move the  stain  by  means  of  a  blotter  and  immediately  put  on 
a  drop  or  two  of  solution  B.  Pull  the  fibres  apart  and  distrib- 
ute them  by  means  of  needles  as  before  and  drop  on  a  cover 
glass  or  thin  microscope  slide.  Any  excess  of  solution  B  should 
be  removed  by  absorbing  it  with  moist  blotting  paper.  This 
stain  is  also  selective  in  its  action,  the  colors  produced  being  as 
follows :  * 


ESTIMATION  OF  FIBRE   CONTENT  391 

Red  or  brownish  red:  Cotton,  linen,  hemp,  ramie. 

Dark  blue:  Bleached  soda  pulps  from  deciduous  woods. 

Bluish  or  reddish  violet:  Bleached  sulphite  fibres  and  the 
thoroughly  cooked  part  of  the  unbleached  sulphite. 

Greenish:  Jute,  manila  and  the  more  lignified  fibres  in  un- 
bleached sulphite. 

Yellow:  Ground  wood. 

As  with  the  Herzberg  stain  this  one  should  be  adjusted  by  trial 
on  known  mixtures  of  fibre  until  it  shows  satisfactory  differ- 
ences in  color.  The  two  solutions  should  be  protected  against 
evaporation  and  dust  but  light  does  not  change  their  staining 
properties  to  any  extent. 

In  estimating  the  fibre  content  of  a  paper  no  account  is  taken 
of  the  size,  clay,  alum,  etc.,  which  may  be  present;  the  paper  is 
therefore  considered  as  being  all  fibre  and  the  sum  of  the  per- 
centages of  the  various  kinds  is  made  to  equal  100  per  cent. 
The  estimation  should  be  based  on  the  examination  of  at  least 
two  samples  of  fibre  removed  from  the  test  tube  and  in  some 
cases  where  especial  accuracy  is  desired  it  is  well  to  examine  four 
separate  slides.  A  set  of  standard  samples  containing  known 
percentages  of  the  different  ingredients  is  very  useful  in  making 
comparisons  with  unknown  samples  and  should  be  used  occa- 
sionally to  refresh  the  judgment  of  the  analyst. 

There  are  two  methods  of  determining  the  percentage  of  the 
various  fibres,  one  is  the  "count  method/'  while  the  other  is 
known  as  the  "  estimation  method."  In  the  first  method  the 
fibres  of  each  kind  are  counted  and  from  the  figures  obtained 
the  percentage  of  each  is  calculated.  The  estimation  method 
depends  upon  the  comparison  of  the  unknown  sample  with 
standard  mixtures  of  known  composition.  The  accuracy  of 
this  method  depends  upon  the  experience  of  the  analyst  and 
upon  continual  reference  to  the  known  standards.  It  is  prob- 
ably fully  as  accurate  as  the  count  method,  is  considerably 
quicker,  and  is  much  easier  to  teach  to  a  beginner.  For  these 
reasons  it  is  usually  preferred  to  the  count  method.  In  using 


392  PAPER  TESTING 

either  method  it  is  quite  obvious  that  the  analyst  must  be  thor- 
oughly familiar  with  the  size,  shape,  and  markings  of  the  various 
fibres  and  with  the  appearance  of  any  ducts,  cells,  or  foreign 
matter  which  habitually  accompany  them.  Without  such  knowl- 
edge it  is  useless  to  attempt  to  make  a  fibre  analysis. 

A  third  method  has  recently  been  proposed  by  Spence  and 
Krauss  *  to  enable  an  estimation  to  be  made  of  the  different 
kinds  of  fibres  in  a  mixture  containing  such  fibres  as  hemlock, 
beech,  poplar,  birch,  maple,  etc.  Four  samples  are  made  up 
by  the  method  of  Spence  and  Krauss  already  given.  Each 
slide  is  examined  under  the  microscope  and  the  lengths  of  the 
various  fibres  are  measured  in  terms  of  the  diameter  of  the 
observed  field.  The  magnification  recommended  is  160  diam- 
eters and  an  adjustable  stage  is  essential  in  order  to  cover  sys- 
tematically the  entire  sample  on  each  slide.  After  all  four 
samples  have  been  examined  the  figures  are  added  together  to 
get  the  total  length  of  each  kind  of  fibre  present.  This  total 
length  multiplied  by  a  weight  factor,  which  varies  with  different 
kinds  of  wood,  gives  a  set  of  directly  comparable  results  which 
may  be  converted  into  the  per  cent  of  each  kind  of  fibre  present. 
The  weight  factors  given  are  as  follows:  rag  pulp  i;  hemlock 
pulp  0.870;  poplar  pulp  0.454;  birch  pulp  0.652;  beech  pulp 
0.525;  maple  pulp  0.365.  Where  a  mixture  of  fibres  from 
deciduous  woods  is  under  examination  the  number  of  counts  of 
each  kind  to  which  the  weight  factor  is  to  be  applied  may  be 
determined  from  an  examination  of  the  number  of  ducts  present. 
It  was  found  that  the  proportion  of  ducts  and  fibres  in  different 
woods  was  as  follows : 


Per  cent  ducts 

Per  cent  fibres 

Poplar  

C  .0 

94.1 

Birch 

2    A 

Q7   6 

Beech 

4.  Q 

QC   i 

Maple                                     

2    3 

07  .7 

1  Spence  and  Krauss:  Paper  20,  1917,  May  23,  p.  n. 


UNBLEACHED   SULPHITE  DETERMINATION  393 

This  method  is  too  slow  to  be  used  where  many  routine 
analyses  are  to  be  made  daily  but  its  accuracy  recommends  it 
particularly  for  settling  cases  of  dispute  between  different 
authorities. 

Unbleached  Sulphite  Determination.  The  method  given  is 
that  worked  out  by  Bright.1 

"The  principle  of  the  method  is  first  to  stain  the  fibres  with 
Cross  and  Bevan's  ferric  ferricyanide  solution,  which  colors  the 
unbleached  sulphite  green,  on  account  of  the  lignin  contained 
in  it,  and  leaves  the  bleached  sulphite  colorless.  This  alone 
gives  a  good  distinction,  but  by  subsequently  staining  with  a 
red  substantive  dyestuff,  the  green  of  the  unbleached  is  changed 
to  a  very  pure  blue,  the  bleached  being  colored  red,  thus  giving 
a  most  striking  contrast. 

"  The  problem  is  to  adjust  the  treatment  with  the  two  solu- 
tions to  bring  out  the  sharpest  contrast.  If  the  treatment  with 
red  is  too  severe,  some  of  the  unbleached  fibres  are  likely  to  be 
colored  purplish,  or  in  extreme  cases  take  on  a  dull,  dirty  red 
color.  On  the  other  hand,  if  the  treatment  with  ferric  ferricy- 
anide is  continued  for  too  long  a  time  or  at  too  high  a  tempera- 
ture, the  reagent  has  a  tendency  to  decompose  and  form  a 
deposit  on  the  slide  as  well  as  on  the  bleached  sulphite,  so  that 
the  latter  turns  a  dull  purplish  color  when  subsequently  stained 
with  red. 

"The  results  depend  on  three  factors  —  namely:  (i)  the  con- 
centration of  the  solution,  (2)  the  temperature  at  which  each 
is  applied,  and  (3)  the  length  of  time  each  is  allowed  to  act. 

"  The  solutions  are  prepared  according  to  the  following  pro- 
cedure: 

Ferric  Ferricyanide 

Sol.  A.  —  N/ioFeCl3  —  2.7  grams  FeCl3  6H2O  per  100  c.c. 
Sol.  B.  —  N/io  K3Fe  (CN)6  -  3.29  grams  per  100  c.c. 

"  After  diluting  to  the  mark  with  distilled  water,  filter  through 
dry  filters  into  clean,  glass-stoppered  bottles  —  protect  from 
dust. 

1  Bright:  Paper  20,  1917,  Aug.  29,  p.  n. 


394  PAPER  TESTING 

"  Equal  volumes  are  mixed  fresh  whenever  the  reagent  is  used. 

Substantive  Red 

Benzopurpurin  4!}  extra  (Bayer  Co.) gm.  0.4 

Oxamine  brilliant  red  BX  (Badische  Co.) gm.  o.  i 

Distilled  Water c.c.  100 

"  Have  the  water  hot  and  stir  in  the  dyes  slowly. 

"  The  stain  is  placed  in  a  tall,  narrow,  cylindrical  beaker,  which 
is  set  into  a  water  bath.  The  slides  are  suspended  in  the  beaker 
by  a  clamp  which  holds  them  at  their  upper  ends,  the  clamps 
resting  across  the  top  of  the  beaker.  A  thermometer  is  sus7 
pended  in  the  beaker  of  stain  beside  the  slides.  The  beaker 
should  be  as  small  as  possible  so  as  not  to  use  up  too  much 
stain  at  one  time. 

"  Staining  with  ferric  ferricyanide  is  done  as  follows: 

"  Mix  equal  volumes  of  two  fresh  solutions  and  heat  to  35°  C. 
regulating  the  waterbath  so  that  it  will  remain  within  i  deg.  of 
the  temperature  named,  for  15  minutes.  The  dry  slide  is  then 
dipped  in  water  to  moisten  it  uniformly,  so  that  air  bubbles 
will  not  be  formed  when  it  is  immersed  in  the  stain.  If  air 
bubbles  are  formed  the  fibres  under  the  bubbles  will  not  be 
stained.  If  dipping  in  water  still  leaves  bubbles,  they  can  be 
removed  by  blowing  across  t-he  slide  from  the  edge.  The  slide 
is  then  suspended  in  the  stain  and  left  there  for  15  minutes  at 
35°  C.  It  is  then  removed  and  washed  by  dipping  in  and  out 
of  a  beaker  of  distilled  water  six  times  and  repeating  the  proc- 
ess in  a  fresh  beaker  of  water.  The  slide  can  then  be  placed 
wet  into  the  red  solution,  but  it  is  perhaps  best  to  dry  it  out 
so  that  the  fibres  will  be  stuck  on  tightly  again  in  case  they  have 
been  loosened  to  any  extent  by  the  treatment. 

"  Staining  with  the  substantive  red  solution  is  done  as  fol- 
lows: 

"  A  fresh  solution  is  heated  to  45°  C.,  and  the  slide,  after  mois- 
tening and  excluding  bubbles  as  before,  is  suspended  in  the  solu- 
tion for  five  minutes  at  45°  C.  and  immediately  washed  in  two 
beakers  of  distilled  water. 


MACHINE   DIRECTION  395 

"The  slide  is  then  dried  and  a  cover  glass  placed  on  with  a 
drop  of  balsam. 

"  To  get  the  clearest,  brightest  results,  distilled  water  must  be 
used  throughout,  and  the  staining  solution  must  be  fresh.  The 
two  solutions  for  ferric  ferricyanide  will  keep  well  if  placed  in 
separate  bottles.  Equal  volumes  are  mixed  together  immedi- 
ately before  using.  The  red  solution  should  be  made  freshly 
each  time  for  the  best  results,  as  it  gets  thick  and  stringy  on 
standing,  especially  when  it  is  being  heated  up  continually. 

"  This  method  of  staining  will  in  general  give  a  distinction  be- 
tween pure  cellulose  fibres  and  those  which  contain  lignin. 
Rags,  bleached  sulphite,  soda  pulp  or  any  thoroughly  bleached 
materials  are  stained  red,  while  unbleached  sulphite,  ground 
wood,  jute,  or  any  lignified  materials  are  stained  blue." 

Physical  Tests 

Machine  Direction.  Several  methods  are  available  for  de- 
termining the  machine  direction  in  a  sample  of  paper.  It  may 
sometimes  be  ascertained  by  mere  inspection  of  the  sheet,  as 
the  formation  noted  on  looking  through  it  is  often  conclusive 
to  the  trained  observer. 

The  usual  machine  wire  imparts  to  the  sheet  of  paper  a  "wire 
mark"  consisting  of  a  series  of  diamond-shaped  marks,  the  long 
diagonal  of  which  points  in  the  machine  direction.  If  the  wire 
mark  is  sufficiently  prominent  so  that  its  direction  can  be 
determined  this  will  establish  the  machine  direction. 

If  the  paper  is  well  sized  and  a  circular  piece  is  cut  out  and 
moistened  on  one  side  by  floating  on  water,  it  will  tend  to  roll 
up  into  a  cylinder  whose  axis  is  in  the  machine  direction  of  the 
sheet.  If  the  paper  is  unsized  it  will  become  entirely  soaked 
through  on  floating  on  water  and  will  not  curl  up.  This  may 
be  avoided  by  sizing  the  paper  with  an  alcoholic  solution  of 
rosin,  or  with  a  solution  of  gelatine  in  water,  drying  and  then 
making  the  test. 

Another  method  of  determining  the  machine  direction  is  to 
cut  two  narrow  strips  of  the  paper,  one  from  either  direction, 


396  PAPER  TESTING 

place  these  one  over  the  other  and  hold  them  upright  in  the 
fingers.  They  will  droop  over  of  their  own  weight  and  if  they 
cling  close  together  the  under  strip  is  in  the  machine  direction 
while  if  the  under  strip  falls  away  from  the  upper  the  latter  is  in 
the  machine  direction. 

The  form  of  the  break  made  by  the  Mullen  tester  shows  the 
machine  direction,  as  the  longest,  or  chief,  line  of  rupture  is 
always  across  the  sheet.  This  is  shown  in  Fig.  43,  which  illus- 


FIG.  43.    LINES  OF  RUPTURE  IN  MULLEN  TEST 

trates  four  typical  ruptures  and  in  which  the  arrows  indicate  the 
machine  direction. 

Wire  or  Felt  Side.  In  many  cases  this  may  be  determined 
very  easily  by  a  simple  inspection  but  in  some  papers  the  wire 
marks  do  not  stand  out  at  all  plainly.  Sometimes  they  may  be 
made  more  prominent  by  plunging  the  sample  for  a  moment 
into  water  and  draining  or  blotting  off  the  excess.  The  moist- 
ure causes  the  fibres  to  expand,  thus  undoing  the  work  of  the 
calenders  and  restoring  the  texture  of  the  sheet  as  it  left  the 
machine  wire.  Inspection  of  a  sheet  thus  dampened  will  often 


WEIGHT  OF   SAMPLE 


397 


show  that  the  wire  marks  stand  out  plainly,  where  before  they 
were  indistinguishable.  This  method  very  often  proves  satis- 
factory even  for  coated  papers. 

Weight  of  Sample.  The  weight  of  a  sample  of  paper  is  usu- 
ally expressed  as  so  many  pounds  per  ream  of  a  given  size,  but 
the  number  of  sheets  per  ream  and  the  standard  size  of  the  sheet 
are  more  or  less  variable  in  the  different  branches  of  the  in- 


FIG.  44.    BEAM  TYPE  OF  PAPER  SCALE 

dustry.  Where  a  full  sheet  of  paper  is  available  the  weight 
per  ream  may  be  conveniently  found  on  scales  of  the  type 
shown  in  Fig.  44.  The  folded  sheet  is  placed  on  the  hooks 
and  the  weight  per  ream  is  shown  by  the  position  of  the  sliding 
poise  on  the  beam.  This  instrument,  which  is  largely  used  for 
mill  work,  is  usually  graduated  for  reams  of  both  480  and  500 
sheets. 

Two  representative  scales  of  the  quadrant  type  are  shown  in 
Fig.  45  and  Fig.  46.     With  these  the  weight  per  ream  in  pounds 


FIG.  45.    "  QUICK-STOP  "  PAPER  SCALE 
Courtesy  of  B.  F.  Perkins  6°  Son,  Inc. 


(398) 


FIG.  46.    BASIS-WEIGHT  SCALE 
Courtesy  of  Thwing  Instrument  Company 


THICKNESS 


399 


per  500  sheets  is  read  off  directly  on  the  scale  and  no  movement 
of  weights  is  necessary. 

In  the  case  of  very  small  samples  a  piece  of  known  area 
should  be  weighed  on  a  chemical  balance  and  the  ream  weight 
calculated  by  the  following  formula: 

(Wt.  in  grams)  X  (1.103)  X  (area  of  trade  size  desired) 

Area  of  sample  in  square  inches 
=  Weight  on  trade  size  desired. 

Thickness.  The  thickness  of  a  paper  may  best  be  deter- 
mined by  means  of  a  spring  micrometer  having  a  hand  that 


FIG.  47.    THICKNESS  GAUGE 
Courtesy  of  B.  F.  Perkins  &  Son,  Inc. 


travels  around  a  circular  dial  which  is  graduated  in  thousandths 
of  an  inch.     One  of  the  many  such  instruments  is  shown  in 


400  PAPER  TESTING 

Fig.  47.  This  type  of  tester  should  not  be  read  closer  than  half 
a  thousandth  as  this  is  about  their  limit  of  accuracy. 

Thickness  may  also  be  measured  by  means  of  an  ordinary 
micrometer  caliper  but  the  amount  of  pressure  is  not  easily  con- 
trolled unless  it  is  supplied  with  a  ratchet  device  which  prevents 
an  excessive  pressure  being  applied.  This  is  not  so  accurate  as 
the  spring  type  but  is  useful  for  approximate  work  around  the 
mill. 

It  is  advisable  to  have  all  thickness  gauges  tested  before  use. 
This  may  be  done  by  securing  a  set  of  standard  sheet-metal 
leaf  gauges  which  range  from  o.ooi  to  0.015  in.  These  should 
be  used  occasionally  to  make  sure  that  the  instrument  for 
measuring  thickness  remains  accurate. 

It  has  been  suggested  by  the  Committee  on  Paper  Testing 
that  the  relative  compactness  of  papers  be  calculated  as  follows 
for  purposes  of  comparison. 

Thickness  in  thousandths  of  an  inch  X  10,000 

Weight  25  X  40,500 
=  Relative  compactness. 

Bulk.  The  "  bulk  "  of  a  paper  is  the  thickness  of  a  certain 
number  of  pages  and  is  a  factor  which  must  be  taken  into  con- 
sideration in  planning  a  book  which  must  not  exceed  a  definite 
thickness.  It  is  usually  measured  by  making  up  a  " dummy" 
or  cutting  out  short  strips,  piling  them  up  to  the  required  num- 
ber and  measuring  its  thickness  with  the  ordinary  graduated 
sliding  clamp.  In  using  this  the  pressure  used  must  be  speci- 
fied as  heavy,  medium,  or  light  a.nd  this  introduces  an  element 
of  uncertainty  into  the  results. 

The  so-called  "pressure  bulker,"  Fig.  48,  made  by  B.  F. 
Perkins  and  Son  has  been  made  to  eliminate  these  troubles. 
In  this  instrument  the  " dummy"  is  put  under  a  definite  pres- 
sure which  is  read  in  pounds  per  square  inch  on  the  dial  and 
the  thickness  in  inches  is  read  on  a  scale  at  the  side. 

Opacity.  The  opacity  or  translucency  of  a  paper  may  be 
measured  by  the  " Contrast  ratio"  metho'd  using  a  Martens 


OPACITY 


401 


photometer  in  a  specially  constructed  box.1  This  method  in- 
volves a  determination  of  the  difference  in  photometric  bright- 
ness, or  contrast,  between  a  black  and  white  spot  when  covered 
with  the  material  to  be  tested. 


FIG.  48.     PRESSURE  BULKER 

Provided  this  apparatus  is  not  available,  good  comparative 
tests  can  be  made  by  cutting  a  small,  sharp-edged  opening  in  a 
piece  of  cardboard  and  placing  this  over  a  source  of  intense 
light.  Pieces  of  the  paper  are  then  laid  over  the  opening  one 

1  Bureau  of  Standards  Circular  No.  63. 


402 


PAPER  TESTING 


at  a  time  and  the  number  of  sheets  required  to  completely 
obliterate  the  light  is  noted.  By  determining  the  thickness  per 
sheet  the  absolute  thickness  of  the  paper  required  to  obliterate 
the  light  can  be  calculated. 

Gloss  or  Glaze.  An  instrument  to  measure  the  gloss  or 
glaze  of  paper  has  been  devised  by  L.  R.  Ingerscll.1  It  was 
found  that  light  specularly  reflected  from  paper  at  an  angle  of 
57.5  degs.  was  almost  completely  plane-polarized  and  working 
on  this  basis  the  instrument  was  designed  to  measure  the  gloss 


FIG.  49.    INGERSOLL  GLARIMETER 

by  determining  the  fraction  of  the  light  reflected  from  the  paper 
at  an  angle  of  57.5  degs.  which  is  polarized.  In  using  the  in- 
strument, light  from  a  tungsten  .lamp  is  reflected  from  the 
paper  through  a  diaphragm,  part  of  the  opening  of  which  is 
covered  with  a  small  Nicol  prism  and  the  rest  with  a  piece  of 
smoked  glass  which  absorbs  about  one-half  the  light.  The 
beam  then  passes  through  the  eyepiece  which  is  another  Nicol 
prism  mounted  to  rotate  in  a  divided  circle  which  reads  with 
the  aid  of  the  vernier  to  five  minutes  of  arc.  On  looking  into 
the  eyepiece  a  divided  field  is  seen  and  a  measurement  is  made 

1  L.  R.  IngersoU:  Electrical  World,  63,  1914,  645. 


TENSILE   STRENGTH  403 

by  turning  the  divided  circle  until  the  dividing  line  between  the 
two  parts  of  the  field  disappears.  From  the  average  of  a  num- 
ber of  such  measurements  the  percentage  gloss  may  be  found 
by  consulting  a  table  which  accompanies  the  instrument. 

Fig.  49  gives  a  perspective  view  of  the  Ingersoll  glarimeter. 

In  using  this  instrument  it  must  be  remembered  that  the 
results  are  comparable  only  when  papers  of  the  same  color  are 
considered,  since  a  black  paper  having  the  same  glossy  surface 
as  a  white  paper  would  reflect  an  entirely  different  per  cent  of 
light,  due  to  the  absorption  of  the  black  color.  Since  the  great 
majority  of  papers  examined  are  white,  this  limitation  is  not  a 
serious  objection.  , 

Tensile  Strength.  The  tensile  strength  of  a  paper  is  deter- 
mined by  the  load,  in  pounds,  required  to  break  a  strip  of  it. 
The  tensile  strength  machine  best  known  in  the  paper  industry 
is  the  Schopper  tensile  machine,  illustrated  in  Fig.  50. 

In  this  device  a  strip  of  paper  15  mm.  (approximately  H  in.) 
wide  by  180  mm.  long  (approximately  yT\  ins.),  is  clamped  at 
each  end  and  the  clamps  are  moved  apart  until  the  strip  is 
broken.  A  suitable  device  indicates  the  pull  in  kilograms  (ap- 
proximately 2.2  Ibs.)  required  to  break  the  strip.  It  is  recom- 
mended that  the  load  in  kilograms  per  15  mm.  width  strip,  be 
converted  into  pounds  per  inch  of  width  by  the  following 
formula: 

(3.73)  X  (Tensile  strength  in  kg.  per  15  mm.  width) 
=  Tensile  strength  in  Ibs.  per  i  in.  width. 

A  tensile  strength  factor  may  be  determined  by  the  following 

formula : 

^Tensile  strength  in  Ibs.  per  i  in.  width\ 

Weight  25  X  40,500  / 

[  =  Tensile  strength  factor. 

The  usual  factor  for  tensile  strength  is  known  as  the  breaking 
length.  This  is  the  length  of  a  strip  which,  if  suspended  at 
one  end,  would  break  of  its  own  weight.  The  following  formula 
may  be  used  to  determine  the  breaking  length  of  a  sample: 


404 


PAPER  TESTING 

(Tensile  strength  per  i  in.  width)  X  (13, 

(Weight  of  a  sheet  25  X  40,500) 
=  Breaking  length  in  yards. 


FIG.  50.     SCHOPPER  TENSILE  MACHINE 

Stretch.  The  amount  of  elongation  at  the  instant  of  rupture 
of  a  strip  of  paper  under  tension  is  measured  on  the  S chopper 
tensile  strength  machine.  The  result  is  figured  as  a  per  cent  of 
the  total  original  length. 

Bursting  Strength.  There  are  two  general  types  of  apparatus 
used  to  determine  bursting  strength.  One  is  of  the  hydraulic 


TENSILE   STRENGTH 


405 


: 


FIG.  51.    MULLEN  TESTER 


FIG.  52.    DISTRICT  OF  COLUMBIA  PAPER  TESTER 


406  PAPER  TESTING 

type,  in  which  the  paper  is  clamped  against  a  rubber  diaphragm, 
through  which  the  pressure  is  applied  to  a  circular  area  of  the 
paper  measuring  one  square  inch.  The  Mullen  tester,  Fig.  51, 
and  the  District  of  Columbia  paper  tester,  Fig.  52,  are  of  the 
hydraulic  type.  The  second  type  of  bursting  strength  apparatus 
is  of  the  spring  operated  metal  plunger  design,  in  which  the 
paper  is  clamped  between  annular  rings,  through  which  a  spring 
operated  plunger  is  forced.  The  Ashcroft  tester,  Fig.  53,  is  the 
only  one  of  the  above  type  now  on  the  market. 


FIG.  53.    ASHCROFT  TESTER 

The  bursting  strength  to  be  of  greatest  use  must  be  expressed 
in  terms  of  the  weight  of  the  Sample.  This  ratio  of  strength 
to  weight  may  then  be  directly  compared  with  the  strength  ratio 
of  any  other  paper,  if  the  same  standard  size  sheet  is  used  in 
each  case.  The  strength  ratio  is  expressed  as  a  percentage. 

Bursting  strength  X  100 

Strength  ratio  =  TTr  .  . — r-  —r~    ^~          '• \ 

Weight  in  pounds  (on  a  size  25  X  40,500) 

Folding  Endurance.  The  folding  endurance  of  a  paper  is 
measured  by  a  machine  in  which  a  strip  of  paper  is  caused  to 


FOLDING  ENDURANCE 


407 


fold  back  and  forth  upon  itself  until  it  is  worn  through.     The 
Schopper  Folding  Machine,  which  is  the  only  device  so  far 


FIG.  54.    SCHOPPER  FOLDING  MACHINE 

made  to  carry  out  this  test,  is  shown  diagrammatically  in  front 
view,  and  from  above  in  Fig.  54. 

In  making  a  test  the  slot  cut  in  the  thin  metallic  plate  fastened 


408  PAPER  TESTING 

to  the  end  of  the  shaft  (13),  is  brought  exactly  in  line  with  the 
jaws  (7)  and  a  strip  of  paper  cut  accurately,  15  mm.  in  width 
and  100  mm.  in  length,  is  firmly  clamped  between  the  jaws  and 
through  the  slot.  The  paper  is  then  put  under  tension  by  pull- 
ing out  the  shafts  (4)  to  which  the  jaws  are  fastened  by  an 
intermediate  spring  (3).  The  shaft  (13)  is  given  a  reciprocat- 
ing motion  by  the  revolution  of  the  wheel  (19),  and  the  paper 
is  folded  and  refolded  over  the  edges  of  the  slot  in  the  thin 
metallic  plate  and  around  the  rollers  (12),  the  revolving  of 
which  eliminates  friction  between  the  paper  and  the  rollers. 
Twice  in  each  revolution  of  the  drive  wheel  (19),  the  jaws  are 
pulled  out  to  what  may  be  termed  the  maximum  position  and 
the  paper  is  then  under  a  tension  of  1000  grams.  When  the 
slot  in  the  metallic  plate  is  in  line  with  the  jaws  the  test  strip 
is  under  the  minimum  tension  of  approximately  730  grams. 
Most  papers  stretch  slightly  under  these  tensions,  which  are 
thereby  reduced  more  or  less,  with  the  result  that  a  somewhat 
higher  folding  number  is  obtained.  The  paper  is  weakened  in 
the  crease  made  by  the  repeated  folding  and  finally  broken  by 
the  tension.  The  number  of  double  folds  is  automatically 
recorded  on  the  dial  (18). 

The  folding  strength  of  paper  is  dependent  not  only  upon  the 
strength  and  durability  of  the  paper,  but  also  is  very  largely 
influenced  by  the  relative  humidity.  To  perform  this  test  in 
the  most  accurate  manner  it  is  therefore  necessary  to  keep  the 
relative  humidity  constant  for  all  tests.  This  can  only  be  done 
by  the  use  of  a  room  where  the  humidity  is  under  control. 
Where  such  a  room  is  not  available  then  note  must  be  made  of 
the  per  cent  relative  humidity  of  the  air  at  the  time  of  the  test. 
No  tests  should  be  attempted  when  the  humidity  is  either  very 
high  or  very  low.  A  relative  humidity  between  65  and  70 
per  cent  is  most  easily  attained  throughout  the  year  and  is  the 
standard  humidity  recommended. 

The  folding  factor  is  determined  by  the  following  formula: 

Folding  endurance         ^  , ,.      , 
/TT7  .      '  — r  =  Folding  factor. 

(Weight  25  X  40,500) 


TEARING  TEST  409 

The  folding  factor  will  vary  between  about  o.i  and  200. 

The  standardization  of  the  folding  tester  and  the  accuracy  of 
the  results  obtained  have  been  very  carefully  investigated  by 
Veitch,  Sammet  and  Reed  1  who  consider  it  valuable  for  indi- 
cating the  probable  durability  of  paper  and  its  suitability  for 
specified  purposes. 

Tearing  Test.  This  method  of  testing  paper  is  not  yet  stand- 
ardized though  much  interest  has  recently  been  shown  along 
this  line  and  several  methods  have  been  proposed  for  determining 
the  tearing  strength  of  paper. 

Case 2  cuts  a  strip  2  \  ins.  by  i  in.  which  is  slit  lengthwise  for  a 
distance  of  2j  ins.,  leaving  a  distance  of  \  in.  to  be  torn. «  The 
strip  on  one  side  of  the  slit  is  fastened  in  a  clamp  and  to  the 
other  strip  is  suspended  a  small  bucket  into  which  water  is 
allowed  to  flow  until  the  two  strips  are  torn  apart.  The  weight 
of  the  bucket  and  water  in  grams  is  taken  as  the  tearing  resist- 
ance number. 

The  Schopper  tensile  machine  was  used  by  Wells 3  who  removed 
the  weight  from  the  arm  and  used  .only  the  arm  and  the  milled 
screw  with  the  pawls  held  out  of  action.  To  eliminate  the  local 
variation  in  a  single  sheet,  several  samples  from  the  same  sheet 
were  torn  at  once,  half  being  cut  across  and  half  with  the  grain. 
A  speed  of  tearing  of  ij  ins.  per  minute  was  used  and  readings 
taken  every  five  seconds  while  making  a  tear  of  3  ins.  This 
method  was  found  to  give  good  check  results  provided  the  speed 
of  tearing  was  constant. 

A  tearing  tester  recently  devised  by  Thwing  is  shown  in  Fig. 
55.  A  small  sample  of  paper  is  cut  and  punched  by  a  special  die 
and  attached  to  two  pins  one  of  which  is  attached  to  a  movable 
weight  on  an  arm  carrying  a  recording  pen  while  the  other  is 
attached  to  a  motor  driven,  sliding  record  card  holder.  This 
holder  is  caused  to  move  away  from  the  pin  on  the  weight  arm, 
thus  tearing  the  paper  along  the  line  of  perforations.  The  record 

1  Veitch,  Sammet  and  Reed:  Paper,  20,  1917,  May  30,  p.  13. 

2  Case:  J.  Ind.  Eng.  Chem.,  n,  1919,  49. 
8  Wells:  Paper,  23,  750,  Feb.  12,  1919. 


4io 


PAPER  TESTING 


shows  graphically  the  force  in  grams  required  to  tear  the  paper 
between  each  two  perforations,  thus  giving  five  peaks,  the 
average  of  which  is  taken  as  the  tearing  strength. 


FIG.  55.    THWING  TEARING  TESTER 
Courtesy  of  Thwing  Instrument  Company 

Absorbency.  The  absorbent  power  of  a  paper  is  generally 
measured  by  suspending  strips  vertically  with  their  lower  ends 
dipping  into  water  and  noting  the  height  to  which  the  water 
rises  in  ten  minutes.  The  average  for  several  strips  cut  in  both 
directions  should  be  taken  as  the  figure  for  absorption. 

This  method  is  criticized  by  Reed  1  because  it  employs  water 
instead  of  ink  but  still  more  because  it  is  unaffected  by  the  bulk 
or  weight  of  the  paper.  He  proposes  allowing  i  c.c.  of  a  standard 
ink  to  fall  from  a  pipette  upon  the  surface  of  a  4-in.  square  of  the 
blotting  paper  which  is  placed  over  a  tumbler  or  beaker  of 

1  Reed:  J.  Ind.  Eng.  Chem.,  10,  1918,  44. 


PERMEABILITY  TO  AIR  411 

such  size  that  the  edge  of  the  spot  will  not  touch  the  glass.  The 
time  for  the  complete  absorption  of  the  ink  is  recorded.  In  this 
test  attention  must  be  paid  to  the  temperature  of  the  ink,  the 
delivery  time  of  the  pipette,  the  distance  of  the  tip  above  the 
surface  of  the  paper,  and  the  amount  of  liquid  used.  All  of 
these  factors  must  be  standardized  if  comparable  results  are  to 
be  obtained. 

Volumetric  Composition.  The  determination  of  the  volume 
composition  of  a  paper  is  at  best  only  an  approximation  but  it  is 
at  times  desirable  to  carry  it  out.  The  weight  of  a  cubic  centi- 
meter of  the  paper  is  first  ascertained  by  calculation  from  the 
thickness  of  the  sample  and  the  weight  of  a  measured  area.  The 
percentage  by  weight  of  the  various  materials  present,  fibres,  clay, 
size,  etc.,  is  then  determined  in  the  usual  way  and  from  this  the 
weight  of  each  in  a  cubic  centimeter  of  the  paper  is  calculated. 
The  weight  of  each  substance  in  grams  divided  by  its  specific 
gravity  gives  the  volume  occupied  by  it,  and  the  sum  of  all  of 
these  volumes  subtracted  from  i.o  gives  the  volume  of  air  per 
cubic  centimeter  of  paper.  This  method  is  fairly  accurate 
when  only  fibres,  clay  and  rosin  are  present  but  when  other  sub- 
stances are  added,  as  in  coated  papers,  the  problem  becomes  more 
complex  and  the  results  less  reliable. 

If  the  volume  of  air  per  cubic  centimeter  of  paper  is  the  only 
information  needed  it  may  be  obtained  by  determining  the  actual 
specific  gravity  by  weighing  in  air  and  then  in  oil  of  known  dens- 
ity exactly  as  in  making  specific  gravity  determinations  in  water. 
It  will  be  found  necessary  to  expose  the  paper,  submerged  in 
oil,  to  reduced  pressure  for  some  time  in  order  to  be  sure  that 
all  air  is  removed  and  replaced  by  oil. 

Permeability  to  Air.  No  simple  and  accurate  apparatus  for 
measuring  this  property  of  paper  is  available.  Herzberg 1  has 
made  measurements  by  passing  air  through  a  definite  area  of 
the  paper  under  standardized  conditions  and  measuring  the 
amount  passed  by  a  gas  meter  provided  with  a  special  overflow 
to  equalize  the  level  on  the  two  sides  of  the  meter.  This  method 

1  Herzberg:  Mitt.  k.  Materialpriif,  1915,  33,  142-144. 


412  PAPER  TESTING 

doubtless  gives  reliable  comparative  tests  but  the  apparatus  is 
not  of  a  kind  which  is  generally  available. 

In  the  case  of  waxed  or  waterproofed  papers  it  has  been  pro- 
posed by  Seiter  1  to  use  the  paper  as  a  diaphragm  in  a  dialyzing 
apparatus,  placing  ferric  chloride  above  the  paper  and  potassium 
ferrocyanide  below.  The  time  required  for  the  development  of 
Prussian  blue  is  a  measure  of  the  porosity  of  the  paper. 

Grease-Proof  Properties.  The  surest  method  of  determining 
whether  a  paper  is  grease-proof  is  to  place  the  sample  on  a  piece 
of  white  paper,  pour  on  it  a  small  quantity  of  oil  of  turpentine 
and  rub  it  around  with  a  bit  of  absorbent  cotton.  If  the  white 
paper  becomes  stained  with  the  oil  the  sample  is  not  grease- 
proof. 

A  rough  test  for  parchment  papers  is  to  heat  the  sample  mo- 
mentarily over  a  flame  and  note  the  formation  of  blisters.  Pin 
holes  will  prevent  the  formation  of  blisters  while  on  the  other 
hand  the  more  impervious  the  surface  the  more  blisters  will  be 
formed.  This  test  is  not  absolutely  reliable,  as  some  papers  which 
blister  are  not  grease-proof,  while  some  which  do  not  blister  are 
satisfactory  in  this  respect;  it  is,  however,  reliable  in  the  ma- 
jority of  cases. 

Degree  of  Sizing.  For  book  and  magazine  papers  which  are 
ordinarily  not  sized  very  hard  a  sufficiently  accurate  test  may 
be  made  by  floating  a  small  piece  of  the  paper  on  a  bath  of 
ink  and  noting  the  time  required  for  the  ink  to  penetrate  to  the 
upper  surface.  In  this  test  a  standard  ink  should  be  used  and  it 
should  be  thrown  away  when  used  once  and  not  returned  to  the 
bottle.  The  temperature  of  the  ink  has  a  very  great  influence 
on  the  time  of  penetration  and  it  should  be  maintained  within 
half  a  degree  throughout  the  tests.  The  personal  factor  of  course 
plays  a  very  important  part  in  this  test  and  to  make  results 
strictly  comparable  they  should  all  be  obtained  by  the  same  per- 
son. 

Attempts  have  been  made  to  eliminate  the  personal  equation 
by  measuring  the  conductivity  of  the  paper  as  it  is  gradually 

1  Seiter:  Chemist- Analyst  No.  21,  April,  1917. 


DEGREE   OF   SIZING  413 

penetrated  by  an  electrolyte.  Okell 1  applies  the  solution  of 
the  electrolyte  to  both  sides  of  the  paper  in  a  specially  con- 
structed cell  which  permits  of  slight  but  constant  pressure  on 
both  sides  of  the  sheet.  A  slightly  modified  form  of  this  cell  has 
also  been  employed  by  Clark  and  Durgin.2  The  results  obtained 
are  interesting  and  warrant  its  use  for  scientific  investigations 
but  the  apparatus  does  not  appear  well  adapted  to  the  rapid 
work  required  where  a  large  number  of  routine  tests  must  be 
made  in  the  shortest  possible  time. 

For  high  grade  papers,  such  as  surface  sized  writing  papers, 
the  flotation  test  does  not  indicate  sufficiently  well  the  quality 
of  the  sizing.  For  such  papers  the  method  proposed  by  Safnmet 3 
should  be  used. 

This  method  involves  the  drawing  of  a  strip  of  paper  over  the 
surface  of  an  iron  tannate  ink  and  allowing  it  to  drain  and  dry 
naturally.  Upon  examination  of  the  surface  with  a  low  power 
microscope,  a  well  sized  paper  will  show  no  indication  of  the 
fibre  having  absorbed  the  ink.  Any  variation  in  the  depth  of 
color  on  the  surface  will  indicate  a  lack  of  uniform  sizing.  This 
test  may  be  still  further  developed  by  erasing  the  surface  with 
an  ink  eraser  (a  spun  glass  eraser  is  most  suitable)  and  again 
dipping  the  sheet  as  before.  A  paper  well  sized  throughout  the 
sheet  will  show  little  or  no  additional  absorption  of  ink  at  the 
erased  spot.  This  test  is  only  comparative  but  may  be  valuable 
to  a  mill  in  checking  the  daily  progress. 

The  ink  used  for  the  above  test  is  made  as  follows : 

Tannic  acid  (dry) 23. 4  grams 

Gallic  acid  (crystals) 7.7  grams 

Ferrous  sulphate 30.  o  grams 

Dilute  hydrochloric  acid  (U.  S.  P.) 25.  o  c.c. 

Phenol i .  o  gram 

Blue  Dye  (Bavarian  Blue  S.  &  J.  No.  478) 2.2  grams 

Water  to  make  up  to  1000  c.c. ;  allow  to  settle,  and  decant  from  any  sediment. 

NOTE.  —  Any  water-soluble  aniline  blue,  as  methylene  blue,  may  be  used  in 
place  of  Bavarian  blue. 

1  Okell:  Paper,  April  n,  1917,  20. 

2  Clark  and  Durgin:  Paper,  22,  1918,  223. 

3  Sammet:  Bureau  of  Chem.  Circular  No.  107,  also  Paper,  10, 1913,  No.  9,  p.  15. 


414  PAPER  TESTING 

Chemical  Tests 

Moisture  in  Paper.  In  most  cases  the  moisture  may  be  de- 
termined easily  and  accurately  by  weighing  a  sample  into  a 
weighing  bottle  with  a  ground-glass  stopper,  drying  at  100°  to 
105°  C.,  closing  the  bottle,  cooling  in  a  desiccator  and  again 
weighing.  The  loss  in  weight  represents  moisture.  In  no  case 
where  the  work  demands  any  degree  of  accuracy  should  the 
weighing  of  the  dried  paper  be  done  in  the  open  air  because  the 
dry  paper  absorbs  moisture  very  rapidly  from  the  surrounding 
atmosphere. 

This  procedure  is  inaccurate  in  some  cases  where  substances  are 
present  which  lose  water  of  crystallization,  or  of  constitution,  at 
the  temperature  named.  This  is  particularly  true  of  papers  where 
calcium  sulphate  is  used  as  a  filler  or  where  satin  white  is  used  in 
the  coating.  In  these  cases  drying  at  100°  to  105°  C.  expels  three- 
fourths  of  the  water  of  crystallization  of  the  calcium  sulphate 
and  this  loss  gives  an  entirely  fictitious  value  to  the  hygroscopic 
moisture.  In  such  cases  the  only  expedient  seems  to  be  to  dry 
the  samples  to  constant  weight  in  a  desiccator  over  sulphuric 
acid. 

Ash  Determination.  A  sample  of  one  gram  of  the  paper  is 
ignited  in  a  weighed  dish,  over  a  burner,  or  in  a  muffle,  until  all 
carbon  is  burned  off.  The  dish  is  then  cooled  in  a  desiccator 
and  weighed;  the  increase  in  weight  represents  ash  and  by  mov- 
ing the  decimal  point  two  places  to  the  right  it  may  be  expressed 
at  once  as  percentage  of  the  paper  taken. 

If  the  ash  is  to  be  cooled  and  weighed  in  the  dish  the  ignition 
may  be  made  in  porcelain,  platinum  or  any  material  not  changed 
in  weight  by  heating  to  a  bright  red  heat,  but  platinum  will  be 
found  to  be  the  cheapest  in  the  long  run  because  it  cools  quickly, 
is  practically  constant  in  weight  and  above  all  because  the 
ignition  is  more  rapid  than  in  porcelain  or  silica.  Because  of  the 
greater  speed  of  combustion  a  shallow  dish  is  much  preferable 
to  a  crucible  and  a  still  further  gain  may  be  made  by  covering 
the  dish  with  a  curved  piece  of  platinum  foil  which  reflects  the 


ASH  DETERMINATION  415 

heat  downward  but  allows  the  entrance  of  plenty  of  air.  With 
four  such  dishes  it  is  easily  possible  to  weigh  out  twelve  samples, 
ignite,  cool,  weigh  and  record  the  results  within  an  hour. 

The  sample  of  paper  need  not  be  weighed  closer  than  0.005 
gram  except  in  cases  where  extreme  accuracy  is  desired  and  then 
the  sample  should  be  weighed  in  the  bone  dry  condition  in  a 
weighing  bottle.  Meker  burners  have  been  found  very  satisfac- 
tory for  ash  determinations,  being  considerably  more  rapid  than 
the  ordinary  Bunsen.  During  burning  care  must  be  taken  that 
no  ash  is  blown  out  of  the  dish  by  strong  air  currents  as  this  is 
likely  to  take  place  especially  with  the  light,  fluffy  ashes  from 
unloaded  or  lightly  loaded  papers.  This  same  danger  must  be 
guarded  against  when  removing  the  covers  from  the  desiccators 
in  which  the  dishes  are  cooled.  The  use  of  desiccators  may  be 
avoided  and  some  time  saved  by  pouring  the  ignited  ash  into  a 
counterpoised  aluminum  pan  as  soon  as  the  dish  is  cool  enough  to 
avoid  danger  of  loss  from  convection  currents.  The  ash  will  cool 
almost  instantly  and  may  be  weighed  at  once. 

The  ash  as  finally  obtained  includes  all  non- volatile  and  incom- 
bustible matter  in  the  paper.  It  may  come  from  at  least  five 
sources:  i,  materials  in  the  pulps  employed;  2,  the  loading  or 
filling  materials  used;  3,  substances  used  in  coating  or  surface 
sizing;  4,  mineral  coloring  matters  or  pigments;  and  5,  ash  due  to 
alum  and  size.  It  is  possible  that  a  paper  may  have  an  ash 
content  as  high  as  5  per  cent  without  being  loaded  but  if  this 
figure  is  exceeded  it  is  safe  to  say  some  filler  has  been  employed. 
In  this  connection  it  is  interesting  to  note  the  following  percen- 
tages of  ash  in  fibrous  raw  materials  as  given  by  Wrede.1 

Stock  Percentage  ash 

Bleached  linen  half  stuff o.  12-1. 86 

Bleached  cotton  half  stuff o.  24-0.  79 

Unbleached  cotton  half  stuff o.  24-1. 12 

Sulphite,  unbleached o.  48-1 .  25 

Soda 0.36-1.40 

Adansonia 5-  70-7. 19 

Japanese  fibres 2.5 

1  Wrede:  Paper,  Jan.  31,  1912. 


41 6  PAPER  TESTING 

In  coated  papers  the  ash,  of  course,  includes  that  from  the  coat- 
ing as  well  as  from  the  body  stock.  If  it  is  desired  to  examine  each 
separately  the  coating  may  in  most  cases  be  removed  as  described 
under  "amount  of  coating."  The  difference  between  the  total 
ash  and  that  in  the  body  stock  gives  that  present  in  the  coating. 

If  it  is  desired  to  calculate  the  original  amount  of  filler  used, 
or  to  make  any  computations  regarding  the  minerals  in  the 
coating  it  is  necessary  to  determine  the  nature  of  the  mineral 
matters  and  in  certain  cases  the  amount  of  each  present.  This 
is  rendered  necessary  because  the  different  minerals  lose  different 
percentages  of  their  weights  in  passing  from  the  air  dry  to  the 
ignited  condition;  some  of  the  ground  minerals  used  as  fillers 
lose  only  about  i  per  cent,  clay  shows  a  loss  of  around  1 2  per  cent 
while  crystalline  calcium  sulphate  loses  nearly  21  per  cent.  The 
complete  quantitative  analysis  of  an  ash  is  a  rather  complicated 
process  which  can  be  carried  out  successfully  only  by  a  skilled 
chemist.  The  following  simple  tests  may  be  of  use  where  a  com- 
plete chemical  analysis  is  not  considered  necessary. 

Boil  a  little  of  the  ash  with  water,  filter  and  to  the  filtrate, 
acidified  with  hydrochloric  acid,  add  a  few  drops  of  barium  chlo- 
ride solution.  A  white  precipitate  indicates  sulphates. 

Warm  a  little  of  the  ash  with  dilute  hydrochloric  acid  filter 
and  make  slightly  ammoniacal.  Filter  off  any  precipitate,  which 
may  have  formed  and  add  a  little  ammonium  oxalate  solution. 
A  white  precipitate  indicates  calcium. 

In  order  to  be  conclusive  both  these  tests  must  be  pronounced 
as  small  amounts  of  sulphates  may  be  derived  from  the  sizing 
materials  and  a  little  calcium  is  almost  always  present  in  clay. 

Evaporate  a  small  sample  of  the  ash  to  dry  ness  after  having 
moistened  it  with  hydrochloric  acid.  Treat  the  dry  residue  with 
a  little  strong  hydrochloric  acid,  take  up  a  little  of  the  moist 
material  on  a  loop  of  platinum  wire  and  hold  it  in  a  non-luminous 
gas  flame.  Calcium  will  impart  a  red  color  and  barium  a  green 
color  to  the  flame.  If  both  are  present  the  red  color  will  show 
as  soon  as  the  wire  is  placed  in  the  flame  while  the  green  will  show 
with  considerable  persistence  after  the  red  has  disappeared. 


SIZING  MATERIALS  417 

Boil  the  material  moistened  with  strong  hydrochloric  acid  in 
the  above  test,  with  a  little  water,  filter  and  add  a  slight  excess 
of  dilute  ammonia.  A  whitish,  flocculent  precipitate  indicates 
alumina  from  the  clay  used. 

No  simple  test  for  magnesia,  indicating  the  presence  of  talc, 
asbestine  or  similar  minerals,  can  be  given,  as  the  qualitative 
test  for  this  element  is  one  which  requires  more  than  the  ordinary 
skill. 

Retention.  By  retention  is  meant  that  per  cent  of  the  entire 
loading  material  added  to  the  beater  which  appears  in  the 
finished  paper.  To  ascertain  this  determine  the  following  facts: 

P  =  weight  of  pulp  added  in  pounds 
C  =  weight  of  clay  added  in  pounds 
A  =  per  cent  of  ash  in  finished  paper 

Ap  =  per  cent  of  ash  in  pulp 

Wc  =  per  cent  of  water  of  composition  of  clay 

Mp  =  per  cent  moisture  in  pulp 

Mc  =  per  cent  moisture  in  clay. 

s~V 

The  per  cent  of  clay  used  would  then  be  —  —  —  >  or  with  greater 

100  C  (i  —  Mc) 
accuracy  - 


The  retention  may  be  calculated  by  the  following  formulae, 
the  second  being  the  more  accurate. 


100 
Retention  = 


Retention  = 


C  (100  -  A) 

iooP(A  -K) 
C(ioo  -A+K) 


In  this  last  formula  K  is  the  per  cent  of  filler  not  derived  from 
the  loading  added;  an  average  value,  which  may  be  applied  in 
the  above  formula,  is  0.50. 

Sizing  Materials.  In  its  broadest  sense  the  term  "  sizing  "  is 
applied  to  a  number  of  materials  used  in  the  beater,  in  the 
coating  and  in  surface  sizing,  and  satisfactory  qualitative  tests 


41 8  PAPER  TESTING 

must  be  able  to  distinguish  between  these  various  substances 
and  also  to  show  whether  a  paper  is  tub  (surface)  sized  or  not. 

Starch  may  be,  and  frequently  is,  used  for  all  three  purposes 
and  is  applied  either  raw  or  cooked  in  the  beater  and  cooked 
only  in  the  other  two  cases.  The  universal  test  for  starch  is 
to  apply  a  dilute  iodine  solution  to  the  paper  when  a  blue  to 
violet  color  will  appear  if  starch  is  present.  It  is  well  to  confirm 
this  test  by  boning  some  of  the  paper  with  a  little  water,  filter- 
ing and  testing  the  nitrate,  after  cooling,  with  a  few  drops  of 
iodine  solution.  This-  is  necessary  because  hydrocelluloses, 
which  are  only  slightly  soluble  in  boiling  water,  also  give  a  blue 
color  when  brought  into  direct  contact  with  iodine  solution. 
Microscopic  examination  will  show  whether  the  starch  granules 
have  been  burst  by  boiling  or  whether  the  starch  was  used  with- 
out cooking.  If  the  paper  to  be  tested  is  torn  so  that  it  splits 
on  the  edge  before  being  moistened  with  the  iodine  solution  it 
is  generally  possible  to  tell  whether  it  is  surface  sized  or  not. 
If  it  is  surface  sized  only,  the  interior  of  the  sheet  will  remain 
white  while  the  surface  will  turn  blue;  if,  however,  consider- 
able starch  was  used  in  the  beater,  this  is  in  part  cooked  and 
drawn  to  the  surface  by  the  heat  of  the  driers  so  that  the  paper 
has  the  appearance  of  being  surface  sized  when  in  reality  it  was 
not.  Microscopic  examination  of  the  papers  after  treating  with 
iodine  will  sometimes  enable  an  opinion  to  be  formed  though 
it  is  seldom  possible  to  prove  positively  in  such  a  case  whether 
the  paper  is  surface  sized  or  not. 

Casein  may  be  detected  in  paper  by  moistening  the  sample 
with  Millon's  reagent  and  warming  gently  either  over  a  flame 
or  over  an  open  steam  bath.  If  casein  is  present  a  brick-red 
color  will  develop.  In  the  case  of  coated  paper  in  which  much 
satin  white  is  used,  the  alkali  present  determines  the  formation 
of  a  yellow  color.  In  this  case  proof  may  be  obtained  by  moist- 
ening the  paper  first  with  dilute  nitric  acid,  to  neutralize  the 
alkali,  and  then  applying  the  Millon's  reagent  as  before;  tested 
in  this  way  satin  white  coated  papers  will  give  the  usual  red 
color.  Casein  may  also  be  detected  by  boiling  the  paper  with 


SIZING  MATERIALS  419 

water  and  a  few  drops  of  ammonia,  filtering  and  adding  to  the 
filtrate  dilute  acetic  acid  very  gradually.  Casein  will  precipi- 
tate when  the  solution  becomes  very  faintly  acid,  but  it  may 
redissolve  on  adding  a  considerable  excess.  This  test  is  also 
given,  though  usually  less  strongly,  by  rosin,  so  the  precipitate 
should  be  tested  with  Millon's  reagent  to  confirm  the  presence 
of  casein.  Casein  is  seldom  used  except  in  the  coating;  cases 
of  surface  sizing  or  of  its  use  in  the  beaters  are  very  rare. 

Glue  is  sometimes  used  as  an  adhesive  in  coating  papers  and 
in  rare  instances  in  the  beaters;  the  better  grades  known  as 
gelatines  are  used  in  surface  sizing.  If  glue  is  present  alone  it 
may  be  detected  by  boiling  the  sample  of  paper  in  water,  filter- 
ing if  necessary,  and  adding  a  little  dilute  tannic  acid  solution; 
a  grayish,  flocculent  precipitate  indicates  glue.  Casein  is  also 
precipitated  by  tannic  acid  and  the  presence  of  starch  prevents 
the-  precipitation  of  glue  so  that  when  either  casein  or  starch  is 
present  there  is  apparently  no  means  of  proving  the  presence  or 
absence  of  glue. 

Rosin  is  used  almost  exclusively  in  the  beaters  to  impart 
waterproof  properties  to  the  paper.  There  is  no  single  test  of 
a  simple  nature  which  will  demonstrate  positively  the  presence 
or  absence  of  rosin  and  any  judgment  regarding  it  must  be 
based  on  the  indications  of  a  number  of  different  tests.  If  a 
little  ether  is  dropped  onto  a  sheet  of  paper  and  allowed  to 
evaporate  there  will  be  formed,  in  the  case  of  rosin-sized  paper, 
a  ring  of  rosin  at  the  edge  of  the  zone  where  the  ether  evapo- 
rated. This  will  be  absent  in  most  unsized  papers,  and  it  will, 
of  course,  be  formed  in  any  paper  which  contains  any  ether 
soluble  material  besides  rosin. 

Another  test  is  made  by  boiling  a  little  of  the  paper  for  a  few 
minutes  in  glacial  acetic  acid  and  pouring  the  acid  into  a  little 
distilled  water.  A  pronounced  turbidity  indicates  rosin,  but  a 
slight  opalescence  may  be  caused  by  other  soluble  substances 
and  must  be  disregarded. 

A  third  test  is  that  known  as  the  Raspail  reaction.  If  a  drop 
of  concentrated  sulphuric  acid  be  placed  on  the  paper  and  a 


420  PAPER  TESTING 

grain  or  two  of  sugar  added  a  pronounced  raspberry  red  color 
will  develop  with  rosin-sized  papers,  while  with  unsized  papers 
the  color  formed  is  brownish  with  only  a  trace  of  pink.  This 
red  color  is  also  formed  when  albuminous  materials  are  present 
so  they  must  first  be  proved  absent  before  the  test  can  be  con- 
sidered indicative  of  rosin. 

Rosin  Determination.  The  amount  of  rosin  in  a  sample  of 
paper  may  be  determined  most  accurately  by  the  ether-alcohol 
method  described  by  Sammet.1 

"Cut  five  grams  of  paper  into  strips  approximately  one-half 
inch  wide  and  fold  them  into  numerous  small  crosswise  folds. 
Place  the  folded  strips  in  a  Soxhlet  extractor  and  fill  with  acidu- 
lated alcohol  diluted  to  approximately  83  per  cent,  made  by 
adding  to  100  c.c.  of  95  per  cent  alcohol  15  c.c.  of  acidulated 
water  containing  5  c.c.  of  glacial  acetic  acid  to  100  c.c.  of  dis- 
tilled water.  Place  the  Soxhlet  flask  directly  in  the  boiling 
water  of  a  steam  bath  and  extract  by  siphoning  from  six  to 
twelve  times,  according  to  the  nature  of  the  paper.  Wash  the 
alcoholic  extract  of  rosin,  which  may  contain  foreign  materials, 
into  a  beaker  and  evaporate  to  a  few  cubic-centimeters  on  a 
steam  bath.  Cool,  take  up  in  about  25  c.c.  of  ether,  transfer  to 
a  3OO-C.C.  separatory  funnel  containing  about  150  c.c.  of  distilled 
water  to  which  has  been  added  a  small  quantity  of  sodium  chlo- 
ride to  prevent  emulsion,  shake  thoroughly,  and  allow  to  separate. 
Draw  off  the  water  into  a  second  separatory  funnel,  and  repeat 
the  treatment  with  a  fresh  25-c.c.  portion  of  ether.  Combine  the 
ether  extracts,  which  contain  the  rosin  and  any  other  ether-soluble 
material,  and  wash  with  loo-c.c.  portions  of  distilled  water  until 
the  ether  layer  is  perfectly  clear  and  the  line  between  the  ether 
and  the  water  is  sharp  and  distinct.  Should  glue  which  is 
extracted  from  the  paper  by  alcohol  interfere  by  emulsifying 
with  the  ether,  it  may  be  readily  removed  by  adding  a  strong 
solution  of  sodium  chloride  to  the  combined  ether  extracts, 
shaking  thoroughly  and  drawing  it  off,  repeating  if  necessary, 
before  washing  with  distilled  water.  Transfer  the  washed  ether 

1  J.  Ind.  Eng.  Chem.,  5,  732,  Sept.,  1913. 


CHLORINE  421 

extract  to  a  weighed  platinum  dish,  evaporate  to  dryness  and 
dry  in  a  water  oven  at  from  98°  to  100°  C.  for  exactly  one  hour, 
cool,  and  weigh.  This  length  of  time  is  sufficient  to  insure 
complete  drying.  Prolonged  heating  causes  a  continual  loss 
of  rosin. 

Paraffin  Determination.  Weigh  out  enough  of  the  paper  to 
give  a  weighable  amount  of  paraffin,  — •  one  to  two  grams  should 
be  sufficient,  —  and  place  the  sample  in  a  Soxhlet  extraction 
apparatus,  or  an  Erlenmeyer  flask,  fitted  with  a  reflux  condenser. 
Cover  with  gasoline  or  carbon  tetrachloride  and  extract  until  the 
paraffin  is  all  dissolved;  if  the  Erlenmeyer  flask  is  used  a  second 
extraction  with  a  fresh  amount  of  solvent  will  probably  be 'neces- 
sary. Evaporate  the  solution  to  dryness  and  weigh  the  residual 
paraffin.  If  there  is  a  tendency  for  the  paraffin  to  creep  over 
the  edge  of  the  dish  it  may  be  more  satisfactory  to  weigh  the 
paper  after  extraction  and  consider  the  loss  in  weight  as 
paraffin. 

Either  gasoline  or  carbon  tetrachloride  is  satisfactory  from 
the  standpoint  of  solvent  power  but  the  latter  is  to  be  preferred 
because  of  its  non-inflammability.  It  is  also  superior  to  chloro- 
form because  its  fumes  are  not  likely  to  produce  anesthesia. 

Chlorine.  As  generally  spoken  of  in  the  mill  "  chlorine  " 
means  free  chlorine  or  more  often  hypochlorites.  These  are 
tested  for  in  the  stock  in  the  beater  by  adding  to  a  small  sample 
of  it  a  few  drops  of  potassium  iodide  starch  solution.  If  they 
are  present  a  characteristic  blue  color  will  result,  its  depth  being 
somewhat  proportional,  to  the  amount  of  chlorine  present. 

Where  the  finished  paper  is  to  be  examined  it  is  best  to  moisten 
it  with  distilled  water  on  a  glass  plate  and  test  it  with  starch 
iodide  paper. 

It  is  sometimes  desired  to  determine  the  total  chlorine  present, 
including  that  as  hypochlorites,  inorganic  chlorides  and  organic 
chlorides.  This  may  be  accomplished  by  moistening  a  weighed 
sample  of  the  paper  with  a  solution  of  chlorine-free  sodium  car- 
bonate, drying  it  in  a  platinum  crucible  and  then  igniting  cau- 
tiously until  all  the  organic  material  is  completely  reduced  to 


422  PAPER  TESTING 

carbon.  The  soluble  salts  are  then  leached  out  and  the  chlorides 
in  the  solution  are  determined  by  titration  with  N/io  silver 
nitrate  solution. 

Free  Acid  Determination.  Weigh  10  grams  of  the  paper  to  be 
tested,  tear  into  small  pieces,  place  in  a  porcelain  casserole  and 
cover  with  a  small  amount  of  distilled  water.  Heat  gently  for 
an  hour  over  water  bath  or  electric  hot  plate.  Pour  off  water 
and  wash  with  small  quantities  of  distilled  water,-  adding  same 
to  water  extract.  Make  up  to  100  c.c.  according  to  directions 
given  on  page  103  of  Cohn's  Indicators  and  Test  Papers. 

The  solution  is  then  poured  into  a  loo-c.c.  Nessler  tube  (long 
form).  A  similar  tube  is  filled  with  100  c.c.  of  distilled  water  to 
which  has  been  added  two  drops  of  the  litmus  solution.  To  the 
former  is  then  added  tenth  normal  standard  solution  of  caustic 
soda  until  the  color  matches  the  sample.  The  acidity  is  then 
expressed  in  terms  of  SO3. 

Sulphur  Determination.  Sulphur  may  be  present  in  paper  in 
a  number  of  different  forms  and  from  several  causes.  White 
papers  may  be  toned  with  ultramarine,  which  nearly  always 
contains  sulphur,  and  which  evolves  hydrogen  sulphide  in  the 
presence  of  alum  or  acid.  The  use  of  sodium  thiosulphate  as  an 
antichlor  or  the  presence  of  improperly  prepared  sulphite  fibre 
may  also  account  for  the  presence  of  sulphur  compounds. 

The  users  of  tissue  paper  for  wrapping  silver  demand  that  the 
paper  shall  be  free  from  sulphur  and  a  method  for  its  determina- 
tion, based  on  the  stain  produced  on  lead  acetate  paper,  has  been 
worked  out  as  follows:1 

The  apparatus  consists  of  a  5oc>c.c.  round  bottom  flask  with 
a  neck  about  2  ins.  long  and  i  in.  in  diameter.  The  mouth  of 
this  neck  is  ground  to  a  flat  surface  and  on  this  is  placed  a  glass 
tube  about  4  ins.  long  and  an  inch  in  diameter,  the  lower  end 
of  which  is  also  ground  flat  to  fit  tightly  upon  the  upper  surface 
of  the  neck  of  the  flask.  The  whole  is  so  arranged  that  after 
placing  a  piece  of  filter  paper  between  the  two  ground  surfaces, 

1  Sutermeister:  Pulp  Paper  Mag.  Can.,  15,  1917,  1021. 


SULPHUR  DETERMINATION  423 

the  tube  and  flask  can  be  securely  clamped  together  so  that  all 
gas  generated  in  the  flask  must  pass  through  the  filter  paper 
and  then  up  through  the  superimposed  glass  tube. 

The  procedure  for  the  testing  of  tissue  papers  is  as  follows: 
A  sample  of  25  sq.  ins.  is  taken  and  its  weight  determined.  It 
is  then  shaken  up  in  a  wide  mouth  glass-stoppered  bottle  with 
10  c.c.  of  distilled  water;  when  partial  disintegration  has  taken 
place,  another  10  c.c.  of  water  is  added  and  the  shaking  continued 
until  the  paper  has  been  completely  reduced  to  pulp.  The 
larger  part  of  the  pulped  mass  is  now  transferred  to  the  flask 
described  above,  and  the  residue  which  is  left  in  the  bottle  is 
rinsed  into  the  flask  with  a  mixture  of  10  c.c.  of  sulphur-free 
phosphoric  acid  and  20  c.c.  of  water. 

Prepare  turnings  from  the  highest  grade,  pure  stick  zinc,  which 
must  be  free  from  sulphur  and  arsenic.  Treat  one  gram  of  these 
turnings  with  10  c.c.  of  a  dilute  solution  of  copper  sulphate 
containing  about  0.002  gram  actual  copper.  After  a  few  minutes 
all  the  copper  will  have  deposited  and  the  turnings  are  then 
thoroughly  washed  to  remove  every  trace  of  zinc  sulphate. 

The  turnings  are  added  to  the  flask  and  a  wad  of  cotton 
inserted  in  its  neck.  Between  the  two  ground  glass  surfaces  is 
then  clamped  a  piece  of  filter  paper  about  2  ins.  square  which 
has  been  perforated  with  small  pinholes  about  |  of  an  inch  apart 
and  which  just  before  use  is  moistened  with  several  drops  of  lead 
acetate  solution.  Finally  a  loose  wad  of  cotton  is  placed  in  the 
tube  above  the  paper. 

The  flask  is  placed  on  the  steam  bath  and  allowed  to  stay, 
with  occasional  shakings,  for  an  hour.  The  filter  paper  is  then 
removed  from  the  neck  of  the  flask  and  air  dried.  It  is  best 
compared  with  the  standard  test  pieces  by  placing  them  side  by 
side  on  a  piece  of  white  paper  and  covering  them  with  a  thin 
piece  of  clear,  white  glass.  The  standard  test  pieces  are  pre- 
pared by  using  sulphur-free  cotton  in  the  flask  instead  of  the 
disintegrated  paper  and  adding  to  this  definite  volumes  of  a 
very  weak  solution  of  sodium  thiosulphate  whose  strength  is 
accurately  known.  The  sulphur-free  cotton  is  prepared  by 


424  PAPER  TESTING 

boiling  absorbent  cotton  in  weak  caustic  soda  solution  and  wash- 
ing thoroughly  with  distilled  water. 

The  sensitiveness  of  this  test  is  such  that  the  presence  of 
o.oooooi  gram  of  sulphur  in  the  flask  will  give  a  distinct  color  on 
the  lead  acetate  paper.  From  tests  of  a  considerable  number  of 
papers  which  have  been  found  satisfactory  in  actual  practice  it 
has  been  proved  that  tissue  paper  is  safe  for  wrapping  silver- 
ware if  it  does  not  contain  more  than  0.000002  gram  of  sulphur 
per  25  sq.  ins.  of  paper  (about  0.25  gram). 

In  using  this  method  certain  precautions  are  necessary  if 
reliable  results  are  to  be  obtained.  The  sample  to  be  examined 
must  be  kept  away  from  all  dust  and  laboratory  fumes  and  in 
handling  it  in  preparing  the  sample  the  ringers  should  be  scrupu- 
lously clean.  Any  perspiration  on  the  fingers  will  be  sufficient  to 
give  an  incorrect  result  and  it  was  found  by  sad  experience  that 
if  the  fingers  were  run  through  the  hair  while  handling  the  sample 
for  analysis  a  strong  test  for  sulphur  was  obtained.  It  is  quite 
obvious  that  any  sample  which  is  submitted  for  tests  should  be 
taken  from  a  freshly  opened  package  of  paper  and  that  it  should 
be  handled  as  little  as  possible.  To  make  a  test  of  a  sample 
which  has  been  lying  around  an  office  for  some  time  and  which  has 
been  handled  repeatedly  is  merely  a  waste  of  time. 

The  purity  of  the  zinc  employed  must  be  ascertained  by  very 
careful  tests  and  the  same  is  true  of  the  phosphoric  acid.  Other 
acids  should  not  be  substituted  for  phosphoric  acid  unless  they 
are  first  proved  to  be  absolutely  reliable  and  it  has  been  demon- 
strated that  sulphuric  and  hydrochloric  acids  are  not  entirely 
safe. 

The  standard  test  papers,  which  are  prepared  with  known 
amounts  of  sulphur,  must  be  freshly  made  each  time  the  test  is 
carried  out  since  they  are  not  sufficiently  permanent  even  when 
kept  in  tightly  stoppered  bottles  in  the  dark. 

Amount  of  Coating.  It  is  sometimes  desirable  to  determine 
the  percentage  of  coating  on  a  sample  of  paper  or  the  amount 
applied  per  ream.  To  do  this  cut  a  sample  of  some  definite  size 
and  weigh  in  the  air  dry  state ;  soak  this  sample  for  a  few  minutes 


GLUE  OR   CASEIN  DETERMINATION  425 

in  a  dilute  solution  of  ammonium  hydroxide,  remove  it  to  a  glass 
plate  and  loosen  the  coating  by  brushing  carefully  with  a  flat 
camel's  hair  brush  moistened  with  the  ammonia  solution.  Fi- 
nally wash  in  running  water,  air  dry,  and  weigh.  The  difference 
in  weight  represents  the  coating  removed. 

In  some  cases  the  coating  is  so  thoroughly  waterproofed  that 
this  treatment  fails  to  remove  it;  in  such  cases  there  is  no  known 
method  for  determining  its  amount.  Where  the  coating  is  partly 
waterproofed  it  may  be  desirable  to  increase  the  strength  of  the 
ammonia  or  to  warm  it  slightly.  Where  the  coating  is  not  easily 
removed  the  brushing  must  be  done  with  great  care  lest  a  con- 
siderable loss  in  weight  be  caused  by  removal  of  fibrous  material. 
It  is  sometimes  a  question  of  judgment  as  to  whether  a  greater 
error  is  caused  by  failure  to  remove  traces  of  coating  or  by 
rubbing  off  some  of  the  fibres. 

Glue  or  Casein  Determination.  There  is  apparently  no  quan- 
titative method  known  for  the  determination  of  these  substances 
when  they  are  present  together.  Both  materials  contain  nitro- 
gen. If  only  one  be  present  and  the  nitrogen  content  of  the 
original  material  as  added  to  the  paper  be  known  then  by  means 
of  the  nitrogen  determination  the  content  of  glue  or  casein  may 
be  estimated. 

For  the  determination  of  nitrogen  weigh  out  from  three  to  five 
grams  of  the  paper,  cut  into  small  pieces  and  place  in  a  Kjeldahl 
digestion  flask.  Add  10  grams  potassium  sulphate,  0.7  gram 
mercury  and  25  c.c.  of  concentrated  sulphuric  acid;  place  the 
flask  in  an  inclined  position  in  a  hood  with  a  good  draft  and  heat 
below  the  boiling  point  of  the  acid  until  frothing  has  ceased. 
Increase  the  heat  until  the  acid  boils  briskly  and  continue  the 
digestion  until  the  solution  is  colorless  or  pale  straw  yellow. 
Allow  the  contents  of  the  flask  to  cool  and  add  30  c.c.  of  a  4  per 
cent  solution  of  potassium  sulphide.  Next  add  50  c.c.  of  caustic 
soda  solution  (saturated  solution) ,  or  enough  to  make  the  reaction 
strongly  alkaline,  pouring  it  carefully  down  the  side  of  the  flask 
so  that  it  does  not  mix  with  the  contents.  Connect  the  flask  at 
once  with  the  condenser,  shake  to  mix  the  contents  of  the  flask, 


426  PAPER  TESTING 

and  distil  until  all  ammonia  has  passed  over.  Collect  the  dis- 
tillate in  a  flask  containing  a  known  volume  of  standard  acid,  and 
at  the  end  of  the  test  titrate  the  excess  of  acid  with  standard 
alkali,  using  sodium  alizarin  sulphonate  or  methyl  red  as  indica- 
tor. The  end  of  the  condenser  tube  should  dip  below  the  surface 
of  the  acid,  the  distillation  should  require  about  45  mins.  and  the 
distillate  should  amount  to  about  200  c.c.  If  a  few  pieces  of 
granulated  zinc  or  pumice  stone  are  added  to  the  distillation 
flask  bumping  during  the  distillation  may  be  avoided. 

As  a  check  on  the  purity  of  the  reagents  a  " blank  test"  should 
be  made  using  the  same  amounts  of  chemicals  as  in  the  regular 
test  but  adding  no  paper. 

Substract  the  volume  of  alkali  required  to  neutralize  the  dis- 
tillate from  the  volume  required  by  the  blank;  the  difference  is 
the  number  of  cubic  centimeters  of  standard  alkali  equivalent  to 
the  ammonia.  This  number  of  cubic  centimeters  of  tenth  nor- 
mal alkali  multiplied  by  0.0014  gives  the  grams  of  nitrogen  in 
the  sample  taken.  To  convert  this  to  casein  multiply  by  the 
factor  6.3,  and  for  glue  use  the  factor  5.6.  Since  the  percentage 
of  nitrogen  varies  in  different  lots  of  casein  and  glue  these  factors 
should  be  determined,  wherever  possible,  on  the  actual  materials 
used  in  the  paper  being  tested. 

Unbleached  Fibres.  Besides  the  microscopical  method  de- 
scribed elsewhere  it  is  possible  to  detect  unbleached  sulphite  fibre 
by  chemical  means.  If  a  sheet  of  paper  containing  a  small 
amount  of  unbleached  fibre  is  moistened  with  Millon's  reagent 
and  then  warmed  in  the  steam  escaping  from  a  steam  bath  it  will 
be  found  that  the  unbleached  fibres  will  show  up  very  distinctly 
as  brownish  hairs.  If  no  unbleached  fiber  is  present  the  brown 
hairs  are  absent.  From  the  proportion  of  fibres  stained  brown 
it  is  possible  to  make  an  approximate  estimate  of  the  amount  of 
unbleached  fibre  present,  provided  its  quantity  is  not  large. 
Where  the  sheet  is  mostly  unbleached,  or  where  groundwood 
is  present  in  considerable  amount,  the  entire  surface  becomes 
brown  and  no  estimate  of  the  proportion  of  unbleached  fibre  can 
be  made. 


GROUNDWOOD   PULP  427 

Groundwood  Pulp.  For  the  qualitative  determination  of 
groundwood  a  number  of  stains  are  available  and  find  quite 
general  application. 

Aniline  sulphate  stains  groundwood  a  yellow  color,  though  the 
test  is  not  quite  so  sensitive  as  that  with  phloroglucinol.  The 
aniline  sulphate  solution  should  be  prepared  by  dissolving 
5  grams  in  50  c.c.  of  distilled  water  and  acidulating  with  one  drop 
of  concentrated  sulphuric  acid. 

A  very  satisfactory  stain  is  made  by  dissolving  i.o  gram  of 
paranitroaniline  in  405  c.c.  of  distilled  water  and  30.5  c.c.  of 
sulphuric  acid  (sp.  gr.  1.84).  With  groundwood  this  gives  an 
intense  orange  color  which  develops  without  drying  the  sample. 
This  stain  possesses  an  advantage  over  phloroglucinol  in  that  the 
acid  is  not  volatile  and  that  it  does  not  deteriorate  so  rapidly. 

One  of  the  most  generally  used  stains  is  prepared  by  dissolving 
5  grams  of  phloroglucinol  in  a  mixture  of  125  c.c.  of  distilled 
water  and  125  c.c.  of  concentrated  hydrochloric  acid.  This  solu- 
tion should  be  kept  in  the  dark  as  light  affects  its  staining  proper- 
ties to  some  extent.  With  groundwood  this  stain  causes  a  ma- 
genta color,  the  depth  of  which  is  approximately  proportional 
to  the  amount  of  groundwood  present.  A  very  light  shade, 
however,  does  not  necessarily  prove  the  presence  of  groundwood, 
as  partly  cooked  jute,  undercooked  unbleached  sulphite  and 
some  other  fibres  are  also  slightly  colored. 

The  reaction  with  phloroglucinol  has  been  employed  by  Cross, 
Bevan,  and  Briggs  1  as  the  basis  of  a  quantitative  method  for 
estimating  groundwood.  The  necessary  solutions  are: 

1.  2.5  grams  of  pure  phloroglucinol  dissolved  in  500  c.c.  of 
hydrochloric  acid,  sp.  gr.  1.06. 

2.  i  c.c.  of  40  per  cent  formaldehyde  in  500  c.c.  of  hydrochloric 
acid,  sp.  gr.  1.06. 

The  paper  under  examination  should  be  rasped  to  a  loose  pow- 
der but  size  need  not  usually  be  extracted.  Two  grams  of  the 
powdered  sample  are  dried  at  100°  C.,  weighed,  transferred  to  a 
dry  flask  and  covered  at  once  with  40  c.c.  of  phloroglucinol  solu- 

1  Cross,  Bevan  and  Briggs:  Papier  Ztg.,  32,  1907,  4113  and  4479. 


428  PAPER  TESTING 

tion.  The  flask  is  stoppered,  shaken,  and  allowed  to  stand 
several  hours  or  best  over  night.  The  solution  is  next  filtered 
through  a  very  little  cotton  placed  in  a  funnel  and  10  c.c.  are 
measured  out  for  titration.  This  is  diluted  with  20  c.c.  of  hydro- 
chloric acid  (sp.  gr.  1.06),  warmed  to  about  70°  C.  and  the 
formaldehyde  solution  added  from  a  burette  in  lots  of  i  c.c.  at  a 
time.  Allow  to  stand  two  minutes  after  each  addition  and  then 
remove  a  drop  without  filtering  and  place  it  on  a  strip  of  partly 
sized  news  paper.  After  ten  seconds  shake  the  drop  off  and  see  if 
a  red  color  is  produced;  if  it  is,  add  more  formaldehyde  solution 
and  toward  the  end  of  the  reaction  reduce  the  amount  added  each 
time  to  0.25  c.c.  Non-development  of  a  red  color  indicates  the 
end  of  the  reaction.  The  test  paper  is  sensitive  to  a  solution  of 
one  part  of  phloroglucinol  in  30,000. 

A  control  test  should  be  made  with  10  c.c.  of  the  phloroglucinol 
solution  in  exactly  the  same  way  and  the  absorption  of  the 
ground  wood  calculated  from  the  difference  of  the  two  titrations. 
It  should  be  based  on  the  dry  material  taken  for  analysis. 

In  carrying  out  this  test  it  is  essential  that  pure  phloroglucinol 
be  used  and  it  is  well  to  obtain  a  considerable  supply  so  that  its 
uniformity  may  be  assured.  The  proportion  of  sample  to  phloro- 
glucinol solution  must  be  kept  constant  and  the  temperature 
must  be  maintained  at  70°  C.  during  the  titration. 

The  absorption  numbers  of  various  fibres  have  been  found  to 

be  aS  follows:  Percent 

Groundwood 7.  87-8. 15 

Groundwood,  brown 5-52 

Sulphite,  bleached o.  90-1.  oo 

Sulphite,  unbleached o.  90-1. 03 

Esparto o.  50 

Cotton o.  20 

Assuming  an  absorption  number  of  8  per  cent  for  groundwood 
and  i  per  cent  for  sulphite  then 
IPO  (P  -  i.o) 

12     =    j 

8.0  —  i.o 
where      H  =  per  cent  of  groundwood 

•P  =  absorption  value  of  dry  ash-free  fibre  in  sample. 


CHAPTER  XVI 
PRINTING 

In  spite  of  its  title  this  chapter  is  not  a  dissertation  on  the  art 
of  printing  but  is  rather  a  collection  of  facts,  intended  to  throw 
a  little  light  on  the  relation  of  the  paper  maker,  the  printer  and 
the  ink  maker.  It  is  frequently  the  case  that  no  one  of  the  three 
fully  understands  the  troubles  of  the  others  and  this  lack  of 
knowledge  prevents  the  cooperation  which  is  necessary  if  the 
greatest  progress  is  to  be  made.  Fortunately  it  is  becoming 
more  frequent  to  find  mutual  assistance  taking  the  place  of  un- 
justified criticism  and  it  is  this  spirit  of  helpfulness  which  has 
enabled  many  of  the  following  notes  to  be  collected.  Necessarily 
they  relate  chiefly  to  the  use  of  book  and  coated  papers,  since 
it  is  upon  these  papers  that  by  far  the  greatest  amount  of  fine 
printing  is  done. 

Printing  may  be  defined  as  "the  reproduction  of  designs,  char- 
acters, etc.,  on  an  impressible  surface  by  means  of  an  ink  or  a 
pigment  (generally  oily),  applied  to  the  solid  surface  on  which 
they  are  engraved  or  otherwise  formed."1  The  only  "impres- 
sible surface"  which  need  be  considered  here  is  the  paper.  Ac- 
cording to  the  method  of  preparation  of  the  "solid  surface"  the 
various  printing  processes  may  be  classed  under  three  headings: 
(i)  relief;  (2)  intaglio;  and  (3)  planographic.  The  relief  proc- 
esses are  those  in  which  the  printing  surface  stands  up  above  the 
surrounding  ground;  of  this  group  the  half-tone  is  the  most  im- 
portant representative.  Intaglio  engravings  are  those  in  which 
the  design  to  be  printed  lies  below  the  surrounding  surface  of 
the  plate;  the  depressed  lines  or  dots  hold  the  ink  which  is  trans- 

1  Century  Dictionary. 
429 


430  PRINTING 

ferred  to  the  paper  after  the  surface  of  the  plate  has  been  wiped 
clean.  The  old-fashioned  steel-engraving  is  typical  of  the  intaglio 
process.  Planographic  processes  are  those  in  which  the  printing 
is  from  a  flat  surface,  neither  raised  above,  nor  depressed  below, 
the  surrounding  ground.  Lithography  with  its  flat  stone  or  metal 
plate  is  typical  of  planographic  processes. 

Half-Tone  Plates.  For  the  preparation  of  half-tones  a 
" screen"  is  necessary.  This  is  prepared  by  coating  a  sheet  of 
glass  with  a  wax  composition  and  then  ruling  diagonally  upon  it 
fine  parallel  lines  at  exactly  equal  distances  from  each  other.  The 
plate  is  then  treated  with  hydrofluoric  acid,  which  etches  the 
glass  wherever  the  diamond  point  has  removed  the  wax,  and 
after  cleaning  the  plate  an  opaque,  dark  pigment  is  rubbed  into 
the  lines.  Two  such  plates  are  sealed  together  face  to  face,  with 
the  rulings  at  right  angles,  to  form  the  finished  screen.  The  dis- 
tance between  the  lines  varies  from  50  per  inch  for  very  coarse 
work  to  300  for  the  finest. 

What  is  termed  a  screen  negative  is  prepared  by  placing  this 
screen  in  a  camera,  in  front  of  and  near  the  plate,  but  not  in  direct 
contact  with  it,  and  then  photographing,  through  the  screen,  the 
picture,  drawing  or  photograph  to  be  reproduced.  The  lines 
prevent  the  passage  of  light,  and  the  resulting  negative  consists  of 
innumerable  dots  separated  by  the  unexposed  spaces  which  were 
covered  by  the  lines. 

The  metal  plate  which  is  to  form  the  half-tone  block  is  carefully 
planished,  sensitized  with  a  mixture  of  gelatine  and  bichromate  of 
potash,  dried,  and  exposed  under  the  screen  negative  just  as  in 
ordinary  photographic  printing.  Copper  is  used  for  the  best 
plates  while  zinc  is  employed  in  cheaper  work.  The  exposed 
plate  is  then  washed  in  water  which  dissolves  the  gelatine  film 
wherever  it  has  not  been  exposed  to  light.  This  gelatine  picture 
is  heated  and  burnt  onto  the  metal  like  an  enamel  which  protects 
the  metal  at  these  points  during  the  next  step  which  is  etching. 
This  is  done  by  treating  the  plate  with  ferric  chloride  solution 
which  dissolves  away  the  copper  where  it  is  not  protected  by  the 
enamel,  thus  leaving  the  picture  in  relief.  In  order  to  produce 


HALF-TONE   PLATES 


431 


the  best  results  the  plate  must  be  re-etched  locally  and  it  is  in 
this  operation  that  skill  and  judgment  are  most  necessary  on  the 
part  of  the  plate  maker.  The  following  table  shows  the  standard 
depths  for  half-tone  plates  in  thousandths  of  an  inch. 


Tone  values 

55-line 
zinc 

85-line 
zinc 

ioo-line 
zinc 

ioo-line 
copper 

I2o-line 
copper 

133-line 
copper 

I5o-line 
copper 

175-line 
copper 

High  lights  

8 

4-6 

3-2 

2.6 

2-5 

2-3 

2  .  2 

1.8 

Middle  tones  

5 

3-1 

2  .2 

1.8 

1-7 

1.6 

1-4 

I  .O 

Shadows 

•7 

2    2 

I    4 

I  .O 

O.Q 

O.Q 

O    Q 

o  6 

Original  plates  are  seldom  used  where  any  large  number  of 
impressions  are  to  be  made  as  they  soon  wear  out,  necessitating 
the  making  of  entirely  new  plates ;  the  use  of  electrotypes  obviates 
this  difficulty.  These  are  prepared  by  coating  the  original  with 
a  thin  film  of  the  finest  graphite  and  then  taking  an  impression  of 
its  surface  in  wax  or  gutta-percha.  The  graphite  prevents 
sticking  and  allows  the  plate  to  be  removed  from  the  wax,  which 
is  then  placed  in  a  ba.th  of  copper  sulphate  and  coated  electro- 
lytically  with  a  film  of  copper.  Deposit  of  copper  may  be  con- 
tinued until  it  becomes  thick  enough  to  use  as  a  plate  or  a  thinner 
film  may  be  backed  up  by  type  metal.  This  process  allows  any 
number  of  electrotypes  to  be  prepared  from  the  same  original, 
which  insures  a  sufficient  supply  of  plates  for  even  the  largest 
editions.  Where  excessive  wear  is  expected  they  are  sometimes 
faced  with  steel  or  nickel  by  electrolytic  means. 

For  three  color  work  three  half-tone  blocks  have  to  be  prepared, 
one  for  yellow,  one  for  red,  and  one  for  blue.  Three  separate 
photographs  are  taken  through  ray  filters;  the  first  of  these 
absorbs  all  rays  except  those  coming  from  yellow  portions  of  the 
picture,  the  second  does  the  same  for  red  and  the  third  for  blue. 
From  these  three  photographs  three  half-tone  blocks  are  made 
in  the  usual  way  except  that  the  screen  is  turned  at  a  slight  angle 
so  that  when  the  plates  are  printed  one  over  the  other  the  dots 
will  not  fall  exactly  in  the  same  place  but  will  form  little  patches 
of  color  side  by  side. 


432  PRINTING 

Lithography.  The  stones  used  for  lithography  are  certain 
porous  limestones  which  possess  the  property  of  absorbing  either 
water  or  grease  but  which  will  not  take  up  a  greasy  ink  wherever 
they  have  been  moistened.  The  surface  of  the  stone  is  prepared 
by  grinding  it  with  emery  or  sand,  using  a  small  stone  or  Q  cast 
iron  levigator  moved  in  circles  all  over  the  surface,  until  it  is 
perfectly  flat.  The  next  operation  is  polishing  with  pumice 
stone  to  remove  sand  scratches  and  this  is  then  followed  by  a  final 
polishing  with  a  "  snake-stone."  This  completes  the  preparation 
of  the  stone  for  some  kinds  of  work  but  for  others  the  surface  has 
to  be  grained.  This  is  accomplished  by  hand  by  going  over  it 
with  graining  sand  and  a  muller  or  mechanically  by  sprinkling  it 
with  sand  and  rolling  it  with  glass  balls. 

The  design  may  be  placed  upon  the  stone  in  two  ways;  it  may 
be  drawn  on  the  surface  directly  by  a  pen  or  a  brush  or  by  means 
of  a  greasy  crayon,  known  as  " chalk";  or  it  may  be  transferred 
to  the  stone  from  a  design  prepared  upon  suitable  transfer  paper. 
When  the  drawing  is  made  directly  upon  the  stone  it  has  to  be 
in  reverse  so  that  the  final  print  may  be  in  the  proper  position. 
The  next  operation  is  a  treatment  with  a  gum  arabic  solution, 
followed,  after  drying  and  washing,  by  rolling  up  with  ink.  Cor- 
rections are  made  by  a  scraper  and  dirt  is  removed  by  acid  and 
the  stone  is  etched  by  dilute  nitric  acid,  which  acts  only  on  those 
portions  which  are  not  protected  by  ink.  After  etching  the 
stone  is  again  inked,  gummed  and  set  aside  to  dry;  when  wanted 
for  printing  the  gum  is  washed  off  and  the  surface  of  the  stone 
allowed  to  become  saturated  with  water. 

The  principles  of  lithography,  as- very  briefly  outlined,  are  also 
applied  to  modified  processes  such  as  printing  from  plates  of  zinc 
and  aluminum  and  also  in  the  more  recent  offset  process. 

Paper  for  Different  Types  of  Printing.  The  kind  of  paper 
which  should  be  used  on  any  job  depends  on  a  number  of  factors 
which  include  the  kind  of  work  being  produced,  the  skill  of  the 
printer,  the  artistic  education  of  the  customer  and  finally  the 
price  which  he  is  willing  to  pay.  It  is  frequently  the  case  that  the 
quality  of  the  paper  is  determined  by  the  illustrations  which  it 


PAPER  FOR   DIFFERENT  TYPES  OF   PRINTING  433 

is  necessary  to  use  since  type  matter  can  be  printed  successfully 
on  any  paper. 

Half-tones  prepared  from  very  coarse  screens  may  be  used  on 
even  such  poor  paper  as  news  print  but  the  results  obtained  can 
harc^ly  be  called  artistic,  though  they  serve  their  purpose.  As  the 
paper  becomes  better  and  its  surface  smoother  the  screen  may 
be  correspondingly  finer.  It  is  difficult  to  establish  definite 
limits  for  the  screen  which  may  be  used  successfully  with  any 
class  of  papers  since  papers  of  the  same  class  vary  considerably 
in  finish  from  time  to  time  and  according  to  the  mill  in  which 
they  are  made.  Considering  book  papers,  upon  which  most  of 
the  fine  printing  is  done,  the  following  may  be  taken  as  approx- 
imately the  limit  of  fineness  for  the  screen  which  may  be  used 
with  good  success. 

Lines 

Machine  finish  book 1 20 

Super  and  English  finish 133 

Imitation  coated 150 

Dull  and  semi-dull  coated 133 

High  finish  coated 175 

For  the  best  results  in  printing  half-tones,  the  surface  of  the 
paper  must  be  such  that  every  dot  is  perfect.  If  the  paper  is 
rough  many  of  the  dots  will  fall  upon  the  elevated  portions, 
where  they  will  print,  but  enough  will  come  over  depressions, 
where  they  will  not  touch  the  paper,  to  give  a  decidedly  gray 
and  irregular  print.  The  avoidance  of  such  irregularities  is 
the  chief  argument  for  the  use  of  coated  papers. 

The  rotogravure  process  "uses  a  copper  cylinder  on  which 
the  illustration  is  printed  from  a  positive  prepared  without 
the  use  of  a  screen.  The  etching  is  similar  to  that  of  the  half- 
tone plate  but  is  entirely  mechanical.  After  inking  the  excess 
is  removed  from  the  surface  by  a  doctor  which  leaves  the  de- 
pressions filled  with  ink.  The  paper  is  then  pressed  into  these 
inked  portions  by  means  of  a  rubber  roller.  This  process  pos- 
sesses the  advantage  that  papers  of  the  poorest  quality  give 
very  beautiful  results;  even  very  low  grade  news  print  can  be 
depended  on  to  give  illustrations  with  remarkable  depth  of  tone. 


434  PRINTING 

For  lithographic  work  the  paper  should  lie  flat  in  order  to 
avoid  wrinkles  during  printing.  The  filler  used  in  plain  paper 
must  be  free  from  gritty  particles  as  these  cause  etching  of 
the  stones  or  plates.  Where  coated  paper  is  employed,  the 
adhesive  used  in  the  coating  must  be  such  as  to  give  it  water- 
proof properties,  or  rather  insolubility,  so  that  the  dampness 
will  not  cause  the  coating  to  come  off.  If  the  printing  is  from 
zinc  or  aluminum  plates  the  paper  must  be  free  from  any  chemi- 
cals which  might  dissolve  and  cause  etching  of  the  plates. 

Paper  used  for  offset  printing  is  generally  of  an  antique  finish 
though  coated  paper  can  also  be  used.  This  process  was  made 
possible  by  the  use  of  metal  plates.  It  uses  less  ink  than  the 
ordinary  lithographic  process  and  causes  less  wear  on  the  plates 
as  the  latter  do  not  come  in  contact  with  the  paper  but  only 
with  a  rubber  blanket  which  is  used  to  transfer  the  ink  from 
the  plates  to  the  paper.  Paper  for  this  process  must  be  well 
sized  and  have  a  firm,  hard  surface,  free  from  fuzz.  If  the 
paper  is  unsized,  the  damp  blanket  tends  to  remove  fibres  and 
dust  which  are  transferred  to  the  plates  and  cause  fill-up  troubles 
and  dirty  prints.  Freedom  from  wire  and  felt  marks  and  a 
neutral  reaction  are  desirable  properties,  and  the  sheets  must 
be  perfectly  flat  so  that  wrinkles  may  not  form  in  passing  through 
the  press.  Stretching  of  the  sheet  under  pressure  must  also  be 
avoided  as  much  as  possible  as  it  also  causes  wrinkles  to  form. 

Choice  of  Inks.  The  selection  of  a  proper  ink  for  the  paper 
which  is  to  be  used  is  generally  the  key  to  success  in  that  par- 
ticular job.  There  are  comparatively  few  general  rules  to  fol- 
low and  it  is  largely  a  question  of-  skill  and  experience  on  the 
part  of  the  printer.  Even  if  he  uses  good  judgment  in  the 
choice  of  an  ink  type,  his  results  may  turn  out  poor,  for  he  is 
almost  entirely  at  the  mercy  of  the  ink  maker  who  may  use 
inferior  raw  materials  with  little  fear  of  detection.  Ink  is  a 
very  complex  mixture  which  it  is  practically  impossible  to  an- 
alyze with  any  degree  of  accuracy  or  completeness;  moreover 
the  figures  which  can  be  obtained*  are  not  easy  of  interpretation. 
For  these  reasons  it  is  good  policy  to  obtain  inks  from  reliable 


DEFECTS  435 

manufacturers  who  are  known  to  turn  out  good  products  and 
who  are  building  up  or  maintaining  good  reputations. 

Inks  are  composed  chiefly  of  pigments  and  oily  carriers  or 
vehicles.  These  range  from  high  grade  varnishes  in  the  inks 
for  engravings  down  to  low  grade  oils  for  the  cheap  inks  used 
for  news  print.  To  these  ingredients  are  added  numerous  other 
materials  such  as  driers,  softeners,  oil  soluble  colors,  etc.,  each 
of  which  imparts  certain  properties  to  the  ink  and  makes  it 
suitable  for  some  particular  kind  of  work.  The  ink  for  printing 
newspapers,  for  example,  must  dry  by  penetration  and  not  by 
oxidation,  because  the  rapidity  with  which  the  paper  is  handled 
allows  no  time  for  oxidation  to  take  place.  At  the  other  ex- 
treme is  the  ink  for  engravings,  such  as  letter  heads,  etc.,  in 
which  a  very  stiff  varnish  is  used  so  that  the  ink  will  stand  up 
above  the  surface  of  the  paper  and  dry  entirely  by  oxidation. 
Between  these  two  limits  there  are  all  kinds  of  inks  made  up 
for  all  kinds  of  printing;  opaque  inks  for  colored  papers  so 
that  the  color  of  the  paper  will  not  show  through;  transparent 
colored  inks  for  process  work;  double  tone  inks;  those  which 
dry  glossy  and  those  which  dry  with  a  dull  finish,  and  many 
others  for  special  purposes. 

Defects.  It  has  been  stated  by  one  who  has  had  much  ex- 
perience in  both  the  paper  and  the  printing  industries,  that 
fully  70  per  cent  of  the  criticisms  against  paper  are  due  to 
troubles  caused  by  inferior  or  inappropriate  inks.  In  addition 
to  the  selection  of  an  unsatisfactory  ink,  there  are  the  troubles 
caused  by  the  printer  who  finds  his  work  defective  in  some  way 
and  attempts  to  improve  it  by  the  addition  of  some  material  to 
his  ink.  While  the  "dope"  used  may  cure  the  trouble,  it  is,  at 
the  same  time,  likely  to  cause  defects  in  some  other,  and  totally 
unexpected,  quarter.  The  modification  of  inks  is  something 
which  should  be  done  by,  or  under  the  direction  of,  a  man  who 
has  had  years  of  experience  and  even  under  those  conditions 
it  is  apt  to  do  more  harm  than  good. 

There  are,  of  course,  many  defects  which  may  be  present  in 
the  paper  and  which  may  cause  the  printer  serious  trouble. 


436  PRINTING 

Some  of  these  are  so  obvious  that  they  hardly  need  mentioning. 
Among  these  would  be  classed  fuzz  on  the  surface,  and  trimming 
dust  from  the  edges;  these  cause  the  filling  up  of  cuts  and  type 
and  may  give  the  appearance  of  picking  in  half-tone  illustra- 
tions or  heavy  blacks.  Such  defects  make  it  necessary  to  wash 
up  frequently  if  good  work  is  to  be  turned  out  and  in  the  case 
of  coated  papers  often  lead  to  their  rejection  as  weak  coated 
when  in  reality  the  coating  was  amply  strong.  Not  all  cases 
of  fuzz,  however,  can  be  laid  entirely  to  the  paper  criticized,  as 
an  examination  of  the  fuzz  collected  from  the  press  usually 
shows  the  presence  of  some  wool  and  silk  fibres  and  sometimes 
it  is  found  to  be  composed  largely  of  fibres  which  were  not  used 
in  that  particular  paper.  Curling,  wavy  edges  or  a  cockly  sur- 
face are  also  very  readily  detected  in  paper  though  not  always  so 
easily  cured.  They  may  be  caused  by  too  prolonged  beating, 
unsatisfactory  drying  on  the  machine,  defects  in  the  calenders, 
or  variations  in  the  humidity  of  the  surrounding  air.  In  the 
last  case  the  paper  usually  becomes  flat  again  if  it  is  stored  in 
thin  layers  for  a  sufficient  length  of  time  for  it  to  come  to  equi- 
librium with  its  surroundings. 

Lumps  in  paper  are  a  fruitful  source  of  complaint  and  are 
often,  though  not  always,  justly  blamed  on  the  paper.  If  large 
or  thick  they  may  seriously  injure  the  plates  or  even  ruin  them, 
necessitating  the  preparation  of  new  ones.  Lumps  may  be 
caused  by  any  number  of  things;  if  they  are  an  integral  part  of 
the  paper,  they  are  frequently  from  the  growth  of  slime  in  the 
pipes  or  chests,  or  from  strings  of  fibre  which  collect  on  the 
screen  plates  and  finally  drop  off;  or  from  rolls  of  stock  which 
break  away  from  some  doctor  on  the  presses  or  driers.  These 
are  the  fault  of  the  paper  and  nothing  else,  but  there  is  another 
class,  the  blame  for  which  cannot  be  so  definitely  placed.  This 
includes  lumps  which  have  become  fastened  to,  or  pressed  into, 
the  surface  of  the  paper  after  the  latter  has  been  completely 
dried.  Here  there  is  always  the  possibility  that  they  came 
from  something  in  the  press-room  just  as  well  as  from  a  defect 
in  the  paper  mill.  Among  the  complaints  on  record,  are  those 


DEFECTS  437 

relating  to  lumps  composed  entirely  of  fibres  and  printing  ink; 
here  the  fibres  might  have  been  contributed  by  the  paper,  but 
the  ink  must  have  come  from  the  press-room.  In  another  case, 
lumps  of  starchy  material  resembling  cake  were  complained  of; 
some  boy  may  have  thrown  part  of  his  lunch  at  a  fellow  work- 
man, but  it  might  just  as  well  have  been  in  the  press-room  as 
in  the  paper  mill.  In  the  case  where  the  complainant  stated 
that  lumps  of  metal  were  present  in  the  paper  and  on  examina- 
tion they  were  found  to  have  the  appearance  and  chemical 
composition  of  electrotype  metal  it  was  reasonable  to  exonerate 
the  paper  mill. 

Complaint  is  often  made  that  the  ink  strikes  through  the 
paper  and  causes  staining  on  the  other  side.  With  very  fluid 
inks  of  the  double-tone  type  it  is  possible  to  make  them  strike 
through,  but  it  can  be  done  only  by  using  an  excessive  amount, 
far  more  than  would  ever  be  used  even  on  the  heaviest  cuts. 
It  has  been  stated  by  one  ink  manufacturer  that  with  paper 
as  heavy  as  25  X  38  —  70,  the  ink  is  not  made  which  will 
strike  through.  In  nearly  all  such  complaints  the  trouble  can 
be  proved  to  be  offset  provided  enough  of  the  printed  sheets 
are  submitted.  In  some  the  offset  will  coincide  so  exactly  with 
the  print  that  it  might  easily  be  taken  for  soaking  through,  but 
in  others  it  will  be  found  to  be  displaced  uniformly  to  one  side 
of  the  cut,  indicating  that  it  did  not  strike  through  but  that  it 
is  an  offset  from  the  sheet  below  upon  which  the  sheet  in  ques- 
tion did  not  fall  exactly  true.  At  times  the  fact  that  it  is  an 
offset  can  be  proved  by  finding  traces  of  the  pigment  portion  of 
the  ink  upon  the  stained  paper.  Even  though  the  oily  part 
might  strike  through,  it  is  hardly  conceivable  that  the  solid 
pigment  could  be  made  to  do  so.  Tearing  the  paper  so  that 
it  will  split  and  expose  the  inner  part  of  the  sheet  will  prove 
that  the  pigment  has  not  penetrated  far  into  the  paper  and  in 
most  instances  will  show  that  the  stain  is  wholly  upon  the 
surface. 

Offsetting  is  a  well-known  phenomenon  and  is  avoided  in 
the  press-room  by  slip-sheeting.  There  are  certain  well-recog- 


438  PRINTING 

nized  types  of  work  in  which  slip-sheeting  is  necessary  and 
others  in  which  it  is  not  required,  and  so  long  as  papers  fall  in 
their  proper  classes,  offsetting  cannot  be  considered  a  defect 
either  of  the  paper  or  the  ink.  There  are  occasional  abnormal 
cases,  however,  in  which  either  the  paper,  or  the  ink,  or  both, 
may  be  to  blame.  If  the  paper  is  finished  and  packed  very 
dry,  handling  it  may  cause  so  much  electrification  that  the 
sheets  will  cling  to  each  other  as  they  are  piled  up  after  printing. 
This  close  contact  tends  to  increase  offsetting.  Electric  neu- 
tralizers  are  a  great  help  in  eliminating  electricity  from  the 
paper,  while  the  gas  flame  arrangement  attached  to  the  press 
in  such  a  manner  that  the  printed  sheet  passes  over  it  has  a 
tendency  to  prevent  offset.  Both  these  devices  are  in  general 
use  in  the  large  printing  plants. 

Excessive  atmospheric  humidity,  which  greatly  delays  the 
drying  of  the  ink,  is  also  a  cause  which  contributes  toward 
offsetting.  The  use  of  slow  drying  inks  and  the  employment 
of  papers  which  are  so  hard  sized  with  animal  sizing  that  the 
ink  does  not  readily  penetrate  both  tend  to  increase  the  trouble, 
while  greater  porosity  of  the  paper  decreases  it.  In  general  it 
may  be  said  that  the  majority  of  coated  papers  will  offset  seri- 
ously if  not  slip-sheeted,  while  with  machine  finish  and  antique 
papers  such  precautions  are  seldom  necessary. 

The  drying  of  the  ink  is  sometimes  so  slow  that  complaint  is 
made  regarding  the  quality  of  the  paper.  The  only  qualities 
in  the  paper  which  are  known  to  retard  drying  are  lack  of  poros- 
ity, and  in  the  case  of  coated  paper  too  much  of  certain  oils  or 
waxes  in  the  coating.  On  the  other  hand,  atmospheric  condi- 
tions may  hinder  drying  or  the  composition  of  the  ink  may  be 
at  fault;  it  is  a  well-known  fact  that  the  drying  of  an  ink  can 
be  very  greatly  changed  in  either  direction  by  the  proper  ad- 
justment of  the  ingredients.  Poor  drying  sometimes  results 
during  color  work  because  of  the  so-called  "  crystallizing "  of 
the  yellow  which  is  printed  first.  This  trouble  occurs  because  the 
yellow  dries  in  such  a  way  as  to  prevent  the  penetration  of  the 
other  colors  which  consequently  remain  on  the  surface  and  dry 


DEFECTS  439 

very  slowly.  This  defect  in  the  ink  can  be  easily  corrected  if  it 
is  discovered  before  the  job  is  completed,  yet  this  is  not  always 
done  and  then  the  paper  gets  the  blame  unjustly.  Not  only 
is  this  true,  but  at  times  the  printer  complains  to  both  the  paper 
maker  and  the  ink  manufacturer  in  order  to  make  sure  of  a 
rebate  from  one  or  perhaps  both  sources. 

Picking  is  a  defect  of  coated  paper  caused  by  a  deficiency  of 
adhesive  in  the  coating.  This  weakens  the  adhesion  of  the 
mineral  matter  in  the  coating  to  the  body  stock  to  such  an  extent 
that  it  is  overcome  by  the  ink  and  the  coating  is  removed  in 
places  causing  white  spots  in  the  print  and  also  fouling  the 
plates  or  type.  As  already  noted,  some  complaints  of  picking 
are  due  to  dirt  which  collects  on  the  plates  and  prevents  the 
ink  from  coming  in  contact  with  the  paper;  these  are  easily 
distinguished  from  true  picks  by  examination  under  a  strong 
lens  or  a  microscope,  as  they  show  that  the  coating  is  intact  and 
not  ruptured  as  it  is  when  picking  has  taken  place.  Picking  is 
usually  the  fault  of  the  paper  maker  though  this  is  not  always 
true.  If  too  tacky  an  ink  is  used  any  paper  can  be  made  to 
pick,  no  matter  how  strongly  the  coating  may  be  sized.  The 
selection  of  an  ink  of  the  proper  consistency,  or  the  adjustment 
of  its  consistency  to  suit  the  paper,  is  therefore  of  very  great 
importance  in  using  coated  paper.  The  temperature  of  the 
press-room  and  the  ink  also  influence  the  results  very  greatly. 
Most  inks  are  ground  in  No.  i  varnish  and  will  work  properly 
at  70°  F.  At  this  temperature  No.  i  varnish  has  as  much  tack 
as  No.  o  varnish  at  60°  F.,  No.  2  varnish  at  80°  F.  or  No.  3 
varnish  at  90°  F.  The  colder  the  ink  the  more  tacky  it  be- 
comes, hence  picking  is  more  frequent  on  Monday  mornings 
when  starting  work.  Defects  from  this  cause  should  not  be 
blamed  on  the  paper  since  the  trouble  disappears  when  normal 
conditions  are  once  more  established. 

A  result  somewhat  similar  to  the  picking  on  coated  paper  is 
found  very  rarely  in  plain  papers.  This  is  caused  by  dry  froth 
from  the  wet  end  of  the  paper  machine  which  gets  onto  the 
surface  of  the  paper  as  it  is  being  formed  but  does  not  become 


440  PRINTING 

thoroughly  incorporated  with  it.  On  drying  and  calendering 
these  bits  of  froth  are  smoothed  down  so  that  they  do  not  show 
except  on  very  careful  inspection,  yet  they  do  not  adhere  very 
firmly  to  the  sheet  and  are  readily  removed  by  the  inked  plate 
causing  a  white  spot  closely  resembling  those  where  coated 
paper  has  picked. 

In  lithograph  work  it  is  claimed  that  the  paper  sometimes 
causes  the  ink  to  smut  or  to  show  slightly  where  there  should 
be  white  surfaces  only.  This  is  said  to  be  due  to  chemicals  in 
the  paper  which  act  on  the  stones  or  metal  plates  and  cause 
them  to  take  a  little  ink  where  there  should  be  none.  For  this 
reason  it  is  well  to  avoid  the  presence  of  water-soluble  sub- 
stances which  can  in  any  way  affect  the  plates.  In  some  cases, 
however,  this  smutting  is  not  the  fault  of  the  paper  but  of  the 
ink  which  may  be  made  of  dyes  or  lakes  which  are  partly  sol- 
uble in  water  and  are  therefore  taken  up  as  very  light  tints  by 
that  portion  of  the  stone  which  has  been  moistened  This  is 
particularly  likely  to  happen  with  inks  in  which  eosine  or  similar 
dyes  have  been  used.  To  prove  the  presence  of  such  water- 
soluble  colors  in  the  ink,  a  piece  of  the  printed  sheet  may  be 
placed  between  sheets  of  moist,  white  blotting  paper  and  pressed 
for  some  time  in  a  copying  press.  If  water-soluble  dyes  were 
used,  a  distinct  offset  will  be  present  on  the  blotter. 

Another  defect  of  coated  paper  which  is  not  strictly  one  of 
printing,  but. is  closely  allied  to  it,  is  that  of  brittleness  or  poor 
folding  qualities.  This  can  be  avoided  to  a  considerable  extent 
by  the  proper  selection  and  beating  of  the  fibres  for  the  body 
stock  and  by  the  use  of  as  little"  coating  as  is  consistent  with 
obtaining  the  proper  printing  surface.  Much  can  be  done  to 
avoid  the  cracking  of  the  surface  by  the  careful  handling  of 
the  sheets  in  the  folding  and  stitching  machines.  Where  possible 
the  fold  should  be  made  with  the  grain  of  the  paper  and  opera- 
tions should  be  conducted  in  as  damp  an  atmosphere  as  possible 
since  the  damper  the  paper  the  less  it  will  crack  on  folding. 

Grayness  of  the  cut  or  filling-up  of  the  half-tone  screen  are 
things  which  are  occasionally  blamed  to  the  paper.  The  gray- 


DEFECTS  441 

ness  of  an  illustration  is  almost  entirely  a  question  of  ink  selec- 
tion or  adjustment;  it  may  be  possible  to  overcome  it  by  using 
more  ink,  provided  too  much  is  not  used,  or  perhaps  another 
ink  can  be  substituted.  In  case  the  ink  needs  to  be  reduced  a 
black  ink  of  the  desired  consistency  should  be  used  rather  than 
a  varnish,  for  the  latter  may  diminish  the  covering  power  of 
the  pigment  to  such  an  extent  that  the  cut  will  appear  gray. 
Reduction  with  a  liquid  is  also  more  likely  to  result  in  filling 
up  the  plates,  which  necessitates  frequent  clean  ups.  Grayness 
may  also  be  caused  by  too  porous  a  coating  which  absorbs  too 
much  of  the  ink  and  leaves  so  little  on  the  surface  that  it  is  not 
well  covered.  The  froth  pits  which  are  sometimes  prese'nt  in 
poorly  coated  paper  may,  if  present  in  too  great  numbers, 
cause  gray  prints  either  locally  or  throughout  the  cut.  These 
pits  are  caused  by  small  bubbles  which  keep  the  coating  away 
from  the  spot  which  they  occupy  and  when  they  finally  break 
leave  a  depression  or  pit  in  the  coated  surface.  These  are  so 
much  lower  than  the  general  surface  that  the  ink  is  not  forced 
into  all  of  them  and  the  result  is  a  white  spot  where  there  should 
be  a  half-tone  dot  of  ink. 

Filling  up  of  the  half-tone  plates  results  in  a  muddy  cut  in 
which  detail  is  lacking.  This  is  most  frequently  the  result  of 
improper  selection  of  ink  and  can  often  be  corrected  by  sub- 
stituting a  different  quality.  Occasionally  the  paper  may  be 
at  fault  if  its  surface  is  at  all  inclined  to  be  dusty  or  to  allow 
very  minute  fragments  to  break  away  and  become  mixed  with 
the  ink. 

In  some  cases  an  ink  is  supposed  to  dry  with  a  dull,  lustre- 
less surface  instead  of  the  usual  gloss;  such  inks  are  largely 
used  on  the  dull  and  semi-dull  finish  papers.  When  using 
such  inks  it  is  sometimes  observed  that  the  completed  print 
has  a  mottled  effect,  part  of  the  surface  being  dull,  while  the 
rest  is  shiny.  This  shiny  part  is  generally  distributed  quite 
regularly  in  patches  of  moderately  uniform  size,  the  edges  of 
which  gradually  shade  off  from  the  glossy  to  the  dull  surface. 
This  mottled  effect  is  due  to  the  fact  that  part  of  the  sheet  is 


442  PRINTING 

less  absorbent  than  the  rest  and  in  these  less  absorbent  spots 
the  ink  is  obliged  to  stay  upon  the  surface  and  dry  like  a  var- 
nish. The  exact  reason  for  this  trouble  has  not  been  fully  de- 
termined, but  it  probably  goes  back  to  irregular  formation  on 
the  paper  machine.  If  the  fibres  are  more  or  less  bunched  up 
they  will  give  a  surface  with  hills  and  hollows;  this  may  be 
reduced  to  a  plane  surface  by  calendering  but  the  density  of 
the  sheet  must  vary  according  to  the  amount  of  compression  it 
has  undergone  and  its  ability  to  absorb  ink  will  vary  corre- 
spondingly. Where  coating  is  applied  to  a  "wild"  sheet  it  tends 
to  be  thicker  in  the  hollows  than  on  the  elevations  and  when  it  is 
calendered  there  is  again  a  considerable  variation  in  density 
and  porosity.  It  is  quite  probable  that  local  variations  in  the 
sizing  of  the  sheet  are  caused  by  the  weave  of  the  drier  felt 
exerting  more  or  less  pressure  on  the  sheet  as  it  is  dried.  When 
such  a  sheet  is  coated  the  adhesive  is  absorbed  more  completely 
by  the  slack-sized  spots  and  is  held  upon  the  surface  where  it  is 
harder  sized.  When  it  is  calendered  it  appears  to  have  a  uni- 
form finish,  but  wherever  the  sizing  is  harder  than  elsewhere 
the  ink  will  not  penetrate  and  will  dry  with  a  gloss.  It  is  abso- 
lutely certain  that  a  high  gloss  does  not  necessarily  mean  a 
good  printing  surface  although  the  two  are  not  necessarily 
incompatible. 

Closely  connected  with  the  mottled  effect  is  the  excessive 
spread  of  the  double-tone  inks  when  they  are  used  on  certain 
papers.  The  amount  of  adhesive  used  in  the  coating  has  much 
to  do  with  this  for  if  the  coating  is  porous  the  ink  is  absorbed 
without  allowing  any  sidewise  spreading  of  the  oil,  while  if  it 
is  non-absorbent,  because  of  too  much  adhesive,  the  ink  will 
spread  to  an  excessive  extent. 

In  color  work  where  a  number  of  impressions  are  made  at 
intervals  the  question  of  register  is  very  important.  If  the 
size  of  the  sheet  changes  between  impressions  it  is  practically 
impossible  to  make  the  two  colors  coincide  and  a  defective 
job  results.  This  is  often  claimed  to  be  the  fault  of  the  paper 
by  printers  who  believe  that  the  paper  maker  can  treat  his 


DEFECTS  443 

product  so  that  it  will  not  change  dimensions  with  changing 
atmospheric  conditions.  As  an  actual  fact  very  little  can  be 
done  by  the  paper  maker  to  cure  this  trouble  since  it  is  just  as 
inherent  in  paper  to  stretch  when  dampened  as  it  is  for  wood  to 
swell  when  exposed  to  moisture.  If  the  paper  is  sent  out  con- 
taining the  average  amount  of  moisture  which  it  would  be 
expected  to  contain  under  the  conditions  of  the  average  print- 
ing shop,  the  paper  maker  may  be  considered  to  have  done  his 
best  and  the  rest  is  up  to  the  printer.  Seasoning  the  paper  in 
the  press-room  to  bring  it  to  equilibrium  with  its  surroundings 
is  an  excellent  precaution,  particularly  where  constant  humidity 
conditions  are  maintained  in  the  press-room.  If  the  shbp  win- 
dows are  kept  open  so  that  outside  changes  are  transmitted  to 
the  paper,  good  register  is  a  question  of  good  luck  or  of  waiting 
before  making  the  second  impression  until  the  same  weather 
conditions  prevail  as  when  the  first  color  was  applied.  With 
commercial  work,  where  the  job  must  be  completed  at  a  definite 
time,  waiting  is  out  of  the  question,  so  the  single  factor  of  luck 
may  be  said  to  be  the  important  one.  Both  temperature  and 
humidity  control  in  the  printing  shop  are  strongly  recommended, 
if  much  color  work  is  to  be  done.  The  temperature,  if  it  changes 
materially,  will  alter  the  size  and  relative  position  of  the  plates 
enough  to  cause  trouble,  while  the  humidity  has  a  very  great 
effect  on  the  paper.  It  is  interesting  to  note  that  in  shops 
where  air  conditioning  systems  are  installed  color  work  can 
be  done  successfully  during  periods  of  weather  which  completely 
shut  down  shops  of  the  ordinary  type. 


APPENDIX 


SOLUBILITY  OF  ALUMINUM  SULPHATE 

(Poggiale) 

100  parts  water  dissolve  (a)  parts  A12  (SO4)3  and  (b)  parts  A12  (SO4)3  •  18 
H2O  at 


o° 

10° 

20° 

30° 

40° 

60° 

80° 

100° 

a 
b 

31-3 
86.85 

33-5 
95-8 

36.15 
107-35 

40.36 
127.6 

45-73 
167.6 

59-og 
262.6 

73-14 
467-3 

89.11 
1132.00 

INFLUENCE  OF  TEMPERATURE  ON  DENSITY  OF  BLACK  LIQUOR  FROM  THE 
SULPHATE  PROCESS 

(C.  Moe) 


Degrees 
F. 

Specific 
gravity 

Baume 

Specific 
gravity 

Baume 

Specific 
graviiy 

Baume 

Specific 
gravity 

Baume 

2OO 

.0800 

10.7 

190 

I  .0080 

I  .2 

.0840 

II  .2 

I  .  2560 

29.6 

1  80 

0.9800 

I  .OI2O 

1-7 

.0880 

II.7 

I  .2600 

29-9 

170 

0  .  9840 

.0160 

2-3 

.0920 

12  .2 

I  .  2640 

30.3 

1  60 

0.9880 

.O2OO 

2.8 

.0960 

12.7 

I  .  2680 

30.7 

150 

0.9920 

.0230 

3.3 

-0995 

I3-I 

I  .2720 

31-0 

140 

0.9950 

.0260 

3-7 

.1030 

13-5 

.2760 

31-4 

130 

o  .  9980 

.0290 

4-i 

•   -1065 

14.0 

•2795 

31-7 

120 

.0010 

O.2 

.0320 

4-5 

•1095 

14-3 

.2830 

32.0 

1  10 

.0030 

0-4 

.0340 

4.8 

.1125 

14-7 

.2865 

32.3 

100 

.0050 

0.7 

1.0360 

5-o 

•1155 

15.0 

.2900 

32.6 

90 

.0070 

1.0 

1.0380 

5-3 

.Il8o 

15-3 

•2935 

32.9 

80 

.0080 

I  .2 

I  .0400 

5-6 

.  1  265 

15-6 

.2970 

33-2 

70 

.0090 

1-3 

I  .0410 

5-7 

.1230 

15-9 

1.3005 

33-5 

60 

.0100 

i-4 

I  .0420 

5-8 

•1255 

16.2 

1.3030 

33-7 

444 


SOLUTIONS   OF   PURE  ALUMINUM   SULPHATE 


445 


SPECIFIC  GRAVITY  OF  SOLUTIONS  OF  PURE  ALUMINUM  SULPHATE  AT  60°  F. 

From  Beveridge 


Specific 
gravity 

100  liters  of  sulphate  of  alumina  solution  contain 

A1203  kilos 

S03  kilos 

Kilos  sulphate  with 

14  per  cent 
A1203 

15  per  cent 
A1203 

17  per  cent 
A1203 

.005 

0.14 

0-33 

I 

0-9 

0.8 

.016 

0.42 

0.98 

3 

2.8 

2-5 

.026 

0.70 

1.63 

5 

4-7 

4-1 

.036 

0.98 

2.28 

7 

6-5 

'    5-8 

•045 

1.26 

2-94 

9 

8-4 

7-4 

•055 

i-54 

3-59 

ii 

10.3 

9  -1 

.064 

1.82 

4.24 

13 

12  .1 

10.7 

-073 

2  .10 

4.89 

15 

14.0 

12.3 

.082 

2.38 

5-55 

•     15-9 

14.0 

.092 

2.66 

6.  20 

19 

17.7 

iS-6 

.101 

2-94 

6.85 

21 

19  .6 

17-3 

.no 

3.22 

7-50 

23 

21-5 

18.9 

.119 

3-50 

8.16 

25 

23-3 

20.  6 

.128 

3-78 

8.81 

27 

25.2 

22.2 

•137 

4.06 

9.46 

29 

27.1 

23-9 

•145 

4-34 

10.  II 

31 

28.9 

25-5 

•154 

4.64 

10.76 

33 

30.8 

27-3 

-163 

4-90 

11.42 

35 

32-7 

28.8 

.172 

5  •  J8 

12  .07 

37 

34-5 

3°-4 

.181 

5  -46 

12.72 

39 

36.4 

32.1 

-190 

5-74 

13-38 

41. 

38.3 

33-7 

.198 

6.  02 

14.03 

43 

40.1 

35-4 

.207 

6.30 

14.68 

45 

42.0 

37-o 

•215 

6.58 

15-33 

47 

43-9 

38.7 

.224 

6.86 

15-99 

49 

45-7 

40.3 

.232 

7.14 

16.64 

47-6 

42  .0 

.240 

7.42 

17.29 

53 

49-5 

43-6 

.248 

7.70 

17-94 

55 

5i-3 

45-3 

.256 

7-98 

18.59 

57 

53-2 

46-9 

-265 

8.26 

I9-25 

59 

55-i 

48.5 

-273 

8-54 

19.90 

61 

56-9 

50.2 

.281 

8.82 

20.55 

63 

58.8 

51-8 

.289 

9.10 

21  .20 

65 

60.7 

53-5 

•297 

9-38 

21.86 

67 

62.5 

55-1 

•305 

9-66 

22.51 

69 

64-4 

56.8 

.312 

9-94 

23.16 

66.3 

58.4 

.320 

IO.22 

23.81 

73 

68.1 

60.0 

.328 

I0.5O 

24.47 

75 

70.0 

61.7 

1-335 

10.78 

25.12 

77 

71.9 

63-4 

446 


APPENDIX 


VOLUMES  SO2  DISSOLVED  BY  ONE  VOLUME  OF  WATER 


Per  cent 
S02 

2  per 

cent 

2} 

3 

3i 

4 

4* 

5 

si 

6 

6* 

7 

At 

o°C. 

1.6 

2  .O 

2.4 

2.8 

3-2 

3-6 

4.0 

4-4 

4-8 

5-2 

5-6 

10°  C. 

1-13 

1.41 

i-7 

2.O 

2.26 

2-55 

2.83 

3-n 

3-4 

3-68 

3-96 

15°  C. 

o-95 

1.18 

1.42 

1.66 

1.89 

2.13 

2-37 

2.60 

2.84 

3-07 

3-31 

20°  C. 

0.79 

0-99 

1.18 

1.38 

I.58 

1.77 

i-97 

2.17 

2.36 

2.56 

2.76 

30°  C. 

0-54 

0.68 

0.82 

°-95 

1.09 

I  .22 

1.36 

1.50 

1.63 

1.77 

1.90 

40°  C. 

0.38 

0.47 

0.56 

0.66 

0-75 

0.85 

0-94 

1.03 

I-I3 

I  .22 

1.32 

Per  cent 
S02 

7i 

8 

8* 

9 

91 

10 

10} 

12 

14 

IS 

16 

At 

o°C. 

6.0 

6.38 

6,78 

7-2 

7.6 

8.0 

8.38 

9.58 

11.17 

11-97 

12.77 

10°  C. 

4-25 

4-53 

4.81 

5-0 

5-28 

5-66 

5-94 

6-79 

7-92 

8.49 

9.06 

15°  C. 

3-55 

3.78 

4.02 

4.36 

4-59 

4-73 

4-97 

5.67 

6.62 

7.10 

7-57 

20°  C. 

3-oo 

3-15 

3-35 

3-55 

3-74 

3-94 

4-13 

4-73 

5.56 

5-91 

6.30 

30°  C. 

2  .04 

2.18 

2.31 

2-45 

2.58 

2.72 

2.86 

3.26 

3-70 

4.08 

4-35 

40°  C. 

I.4I 

1.48 

1.58 

1.69 

i-79 

1.88 

i-97 

2.26 

2.63 

2.82 

3.00 

Per  cent 
S02 

17 

18 

20 

22 

24 

26 

28 

30 

35 

40 

45 

At 

o°C. 

13-56 

14.36 

15.96 

17-55 

19-15 

20.74 

22.32 

23-94 

27-93 

31.92 

35-91 

10°  C. 

9  .62 

IO.2 

11.32 

12-45 

13-58 

14.71 

15.84 

16.98 

19-81 

22.64 

25-47 

15°  C. 

7-94 

8.57 

9.46 

IO.4O 

n-35 

12  .29 

I3.24 

14.22 

16.58 

18.92 

21.28 

20°  C. 

6.69 

7.09 

7.88 

8.66 

9-45 

IO.24 

11.03 

11.82 

13-79 

I5-76 

17-73 

30°  C. 

4.62 

4-8q 

5-44 

5-98 

6.52 

7.07 

'    7.6l 

8.16 

9-52 

10.88 

12  .24 

40°  C. 

3-19 

3.38 

3.76 

4-13 

4-5i 

4.88 

5-26 

5-64 

6.58 

7-52 

8.46 

Per  cent 
S02 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

At 

o°C. 

39-90 

43-89 

47-88 

53-67 

55-86 

59-85 

63.64 

67.63 

71.82 

75-81 

79-8 

10°  C. 

28.30 

3LI3 

33-96 

36.79 

39-62 

42.45 

45-28 

48.4 

50-97 

53-77 

56.6 

15°  C. 

23-65 

26.01 

28.38 

30-74 

33-n 

35-47 

37-84 

40.20 

42.57 

44-99 

47-3 

20°  C. 

19.70 

21.67 

23.64 

25  .61 

27.58 

29-55 

31-53 

33-50 

35-46 

37-43 

39-4 

30°  C. 

13.60 

14.96 

16.32 

17.68 

19.04 

20.40 

21  .76 

23.12 

24.46 

25.82 

27.2 

40°  C. 

9-40 

10.34 

11.28 

12.12 

13.16 

14.20 

I5-04 

15.98 

16.92 

17.86 

18.8 

COMPARISON  OF  TEMPERATURES  447 

CONVERSION  OF  CENTIGRADE  TO  FAHRENHEIT  DEGREES 


°c. 

°F. 

+°C. 

+°F. 

+°c. 

+°F. 

+°c. 

+°F. 

+°C. 

+°F. 

-30 

—  22  .O 

17 

62.6 

64 

147.2 

Ill 

231.8 

158 

316.4 

29 

2O.  2 

18 

64.4 

65 

149.0 

112 

233-6 

159 

318.2 

28 

18.4 

19 

66.2 

66 

150.8 

H3 

235-4 

1  60 

320.0 

27 

16.6 

20 

68.0 

67 

152  .6 

114 

237.2 

161 

321,8 

26 

14.8 

21 

69.8 

68 

154-4 

"5 

239.0 

162 

323-6 

25 

13.0 

22 

71.6 

69 

156.2 

116 

240.8 

163 

325.4 

24 

II  .2 

23 

73-4 

70 

158.0 

117 

242  .6 

164 

327.2 

23 

9-4 

24 

75-2 

7i 

159.8 

118 

244.4 

165 

329.0 

22 

7-6 

25 

77.0 

72 

161.6 

119 

246.2 

166 

330.8 

21 

5-8 

26 

78.8 

73 

163.4 

1  20 

248.0 

167 

332.6 

2O 

4.0 

27 

80.6 

74 

165  .2 

121 

249.8 

1  68 

334-4 

19 

2  .2 

28 

82.4 

75 

167.0 

122 

251.6 

169 

•336  .  2 

18 

0.4 

29 

84.2 

76 

168.8 

123 

253-4 

170 

338.0 

i? 

+  1.4 

3° 

86.0 

77 

170.6 

124 

255-2 

171 

339-8 

16 

3-2 

31 

87.8 

78 

172.4 

125 

257.0 

172 

341.6 

15 

5-0 

32 

89.6 

79 

174.2 

126 

258.8 

173 

343-4 

14 

6.8 

33 

91.4 

80 

176.0 

127 

260.6 

i74 

345-2 

13 

8.6 

34 

93-2 

81 

177.8 

128 

262.4 

i75 

347-o 

12 

10.4 

35 

95-0 

82 

179.6 

129 

264.2 

176 

348.8 

II 

12  .2 

36 

96.8 

83 

181  .4 

130 

266.0 

177 

350-6 

10 

14.0 

37 

98.6 

84 

183.2 

131 

267.8 

178 

352-4 

9 

15-8 

38 

100.4 

85 

185.0 

132 

269.6 

179 

354-2 

8 

I7.6 

39 

IO2  .2 

86 

186.8 

133 

271.4 

1  80 

356.0 

7 

19.4 

40 

IO4.0 

87 

188.6 

134 

273.2 

181 

357-8 

6 

21.2 

4i 

105.8 

88 

190.4 

135 

275.0 

182 

359-6 

5 

23.0 

42 

107.6 

89 

192  .2 

136 

276.8 

183 

361-4 

4 

24.8 

43 

109.4 

90 

194.0 

137 

278.6 

184 

363-2 

3 

26.6 

44 

III  .2 

9i 

195.8 

138 

280.4 

185 

365-0 

2 

28.4 

45 

II3.0 

92 

197.6 

139 

282.2 

186 

366.8 

I 

30.2 

46 

II4.8 

93 

199.4 

I4O 

284.0 

187 

368.6 

O 

32.0 

47 

II6.6 

94 

2OI  .2 

141 

285.8 

1  88 

370.4 

+  I 

33-8 

48 

II8.4 

95 

203.0 

142 

287.6 

189 

372.2 

2 

35-6 

49 

1  2O.  2 

96 

204.8 

143 

289.4 

190 

374-0 

3 

37-4 

50 

122  .O 

97 

206.6 

144 

291.2 

191 

375-8 

4 

39-2 

5i 

123.8 

98 

208.4 

145 

293.0 

192 

377-6 

5 

41  .0 

52 

125.6 

99 

2IO.2 

I46 

294.8 

i93 

379-4 

6 

42.8 

53 

127.4 

100 

212  .O 

147 

296.6 

194 

381.2 

7 

44.6 

54 

129.2 

IOI 

213-8 

148 

298.4 

195 

383-0 

8 

46.4 

55 

I3I.O 

1  02 

215  .6 

149 

300.2 

196 

384.8 

9 

48.2 

56 

132.8 

103 

217.4 

*5o 

302.0 

197 

386.6 

10 

50.0 

57 

134.6 

104 

219.2 

151 

303-8 

198 

388.4 

ii 

51-8 

58 

136.4 

105 

221  .O 

152 

305-6 

199 

390.2 

12 

53-6 

59 

138.2 

1  06 

222.8 

153 

307-4 

200 

392.0 

13 

55-4 

60 

I4O.O 

107 

224.6 

154 

309-2 

14 

57-2 

61 

I4I.8 

1  08 

226.4 

155 

311.0 

15 

59-0 

62 

143.6 

109 

228.2 

156 

312.8 

16 

60.8 

63 

145-4 

no 

230.0 

157 

314.6 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the 
sion  of  the  editor  and  publishers. 


448 


APPENDIX 


(Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the  permis- 
sion of  the  editor  and  publishers.) 

PHYSICAL  CONSTANTS 


1 

I 

2 

3 

4 

6 

8 

9 
10 
ii 

12 
13 

14 
15 

16 

i? 

18 

iQ 

20 
21 
22 
23 
24 

25 

26 
27 
28 
2Q 
30 
31 
32 

33 
34 

Name 

Sym- 
bol 

Atomic 
weight. 
O  =  i6 

Molec- 
ular 
weight 

Specific  Gravity. 
Water=i. 
Air=i  (A). 
Hydrogen  =i  (D.) 

Atomic 
vol. 
At.wt. 

Specific 
heat 
at  o°  C. 

Sp.Gr. 

Aluminium.  .  . 

Al 

Sb 
A 

A 

As 
As 
Ba 
Bi 
B 
B 
Br2 
Br2 
Cd 
Cs 
Ca 
C 
C 
C 
Ce 
Cl 
Cl 
Cr 
Co 
Cb 

Cu 

Er 
F 
F 
Gd 
Ga 
Ge 
Gl 
Au 

He 

27.1 

1  2O.  2 

39-88 

39.88 
74.96 
74.96 

I37-37 
208 

II  .0 
II  .0 

79.92 
79.92 

I  I  2  .  40 
I32.8I 
40.07 
12.005 
12.005 
12.005 
140.25 
35.46 
35.46 
52.0 
58.97 

93-5 
63-57 
167.4 
19.0 
19.0 

157-3 
69.9 

72.5 
9.1 
197.2 

4.00 

f2.7o8 
\2.72¥° 
6.6900^° 

r  1.379  A.i 
119.96  D.J 
I.4046-1860 
4-7i614° 
5.7271*° 
3-75 
9-7474 
2-45 
2.53-2.68 
5.869i60°  A. 
3.18830° 
8.64217° 
i.8720° 
I-544629-20 
1.75-2.10 
2.10-2.585 
3.47-3-5585 

6.9225° 

2.491°°  A. 

1-4405°° 
6.922° 
8.7i8¥° 
7.o61F 

8.91-8.96 

4-77 
i.3i«°A. 

i  .  i4-187° 
1-31 
5-9524° 
5.46918° 
i.8520° 
19.32 

/  0.1368  A. 
11.98  D. 

IO.OI 

9-96 

18.2 

JO.222O 
0.0495 
0.1233 

0.0758/21°- 
0.08301650 

Antimony 

Argon,  gas 

39.88 

liquid 

28.4 
15.9 
13-1 
36.6 

21.3 
4-5 

4-2 

24-9 
13.0 
71.0 
25-9 

6.2 

5-i 
3-4 
20.3 

24.6 
7-6 
6.8 
13.2 

7-i 
35-i 
"16.7 

I2O.I 

ii.  8 

13-3 

4-9 

10.2 

29.21 
20.  2  / 

Arsenic,  amorph... 
cryst  

299.84 
299  .  84 

Barium 

Bismuth. 

0.03013 
0.3066 

o.i65(21°) 

0.0555(83°) 
0.1071 
0.0548 
0.0522 

o.i453 
0.241 

0.2O2 
0.1469 
O  .  05  1  1  2 
O.I24I 
0.2262 
0.10394 
O.I03O 

Boron,  amorph.  .  .  . 
cryst 

Bromine,  gas  
liquid 

I59.84 
159.84 
1  1  2  .  40 

Cadmium 

Caesium  
Calcium 

Carbon,  amorph... 
fraphite 

iamond  
Cerium  
Chlorine,  gas  
liquid  
Chromium  
Cobalt  [bium) 
Columbium  (Nio- 

Coooer   . 

70.92 

38.0 
38.0 

0.0936 

Erbium  
Fluorine,  gas  
liquid  
Gadolinium  
Gallium  
Germanium  
Glucinum    (Beryl- 
Gold  .[Hum) 

Helium,  gas  

0.079 
0.0737 

- 

4.00 

0.0316 

I.248218° 

PHYSICAL   CONSTANTS   OF  THE   ELEMENTS 


449 


OF  THE  ELEMENTS 


Number  1 

11! 

+j  •  oS 

<&x 

Electrical 
conduc- 
tivity f 
at  o°  C. 

Thermal 

conductivity 
K*  at  o°  C. 
Ag=i.oo 

Linear  coefficient  of 
expansion 

Melting 
point, 

Boiling 
point, 
°C. 

i 

2 

3 

4 

6 

8 

9 

10 

ii 

12 
13 
14 

15 

1  6 

i? 

18 

19 

20 
21 
22 

23 
24 

25 

26 
27 
28 
2Q 
30 
31 
32 

33 
34 

6.  02 

5-95 
4.92 

5  -69 
6.23 

324000 
27100 

28600 

•3435 
.0442 
.043894 

.04245 
.041152 

At  °  C. 
40° 
40° 

657° 
630° 
-187.9° 

>2200° 
1440° 

-186.1° 

•040559 

40° 

<(36°° 
554 
vol.  950° 
1420° 
sublimes  at 
35oo° 

sublimes  at 
850° 
268° 
2200°  in 
vacuo 

6.27 

3-37 
1.82 
4.44 

8-57 
6.16 

6-93 
5-83 
2.89 

2  .22 
1.76 
6.28 
4.40 
8.02 

5-42 
6.08 

9260 

.0177 

.041346 

40° 

.  .  r 

{ 

-v° 

321° 

28.45° 
805° 

sublimes  at 
sublimes  at 
sublimes  at 
635° 

-102° 

58.7 
765-9° 
670° 

146000 
25400 
95000 

.2213 

.043069 
.0339482 

40° 
27-100° 

"40°" 
40° 
40° 

.04054 
.040786 
.o4on8 

35oo° 
35oo 
35oo° 

13950 
83200 

-33-6° 

.021978 

0-10° 

I5200 
1478° 
I9500 

f  I083° 

1  1065    (in  air) 

2200° 
2310°,  200O° 

in  vacuo 

.041236 

40° 
40° 

5-95 

640600 

.7198 

.041678 

-223° 

-187° 

5-53 
5-34 

6.23 

30.15° 
916° 
1280° 
1062° 

<-269° 

"5410020° 
468000 

vol.  1350° 
>i90o° 
2530°,  2000° 
in  vacuo 

-268.75° 

.7003 
•  033386 

.041470 

0-100° 

*  K  =  the  number  of  grams  of  water  which  can  be  raised  from  o°  to  i°  C.  by  the  heat  which 
passes  through  a  cubic  centimeter  of  the  substance  in  one  second  when  the  temperature  of  the 
opposite  sides  of  the  cube  are  maintained  at  a  difference  of  i°  C. 

t  Reciprocal  of  the  resistance  in  ohms  of  a  centimeter  cube  of  the  substance. 


450 


APPENDIX 


PHYSICAL  CONSTANTS 


Number  | 

Name 

Sym- 
bol 

Atomic 
weight. 
0  =  i6 

Molec- 
ular 
weight 

Specific  Gravity. 
Water  =  I. 
Air=i  (A). 
Hydrogen=i  (D.) 

Atomic 
vol. 
At.wt. 

Specific 
heat 
at  o°  C. 

Sp.Gr. 

I 

2 

3 
4 

1 

8 
9 

10 

ii 

12 
13 

14 

15 

16 

17 

18 

19 

20 
21 

22 

23 

24 
25 
26 
27 
28 
29 
30 
31 
32 

33 
34 
35 
36 

H 

39 
40 

Hydrogen,  gas 

H 

1.008 
1.008 

114.8 
126.92 
126.92 
!93-i 
I93-I 
55.84 
55.84 
55.84 
55.84 
55.84 

82.92 

82.92 
i39-o 

207  .  20 
6.94 
24.32 

54-93 
200.  6 
96.0 
144^3 

20.2 

58.68 
I4.OI 
I4.OI 
190.9 

16.00 
16.00 

106.7 

31-04 
31.04 

3!-04 
195-2 
39.10 
140.9 
226.0 

IO2  .9 

85.45 

2.Ol6 
2.OI6 

0.06949  A. 

—252.83° 

0.07105 

745-52mm. 
7.12¥ 

8.72  A. 
4-948170 
15-86 

22  .42 
7-85-7-88 
7.86 

7  .  60-7  .  80 
7.03-7.13 

7.58-7-73 
/2.8i8  A.I 
140.78D.J 
2.i55~152° 

6-I54?9.9, 
n-337iibi 

o.53420° 
1.69-1.75 
7.42 

13-5953' 
io.28i¥ 

6.9563 
r  0.695  A.l 
19.96   DJ 
8.6-8.93 
0.96737  A. 
o.8o42-195-5° 
22.48 
1.10535  A. 
i.iiSi-182-50 
1.658  A. 
11-14-11  .9 
i.83i180 

2  .  29616° 

I.76444-30 
2i.i6¥° 

o.862i20° 
6-4754 

12  .1 
1.53220° 

1.4 
16.1 

25-7 
12.2 

8.6 
7-i 
7-i 
7-3 
7-9 
7-3 

3-  4*° 
>  . 

0.05695 
o.o336206° 
0.04852 

liquid.  .    .    . 

H 

[ndium  

In 
I 
I 

Ir 
Ir 
Fe 
Fe 
Fe 
Fe 
Fe 

Kr 

Kr 
La 
Pb 
Li 
Mg 
Mn 
Hg 
Mo 
Nd 

Ne 

Ni 
N 
N 
Os 
O 
0 
03 
Pd 
P 
P 
P 
Pt 
K 
Pr 
Ra 
Rh 
Rb 

[odine,  gas  

solid  
[ridium,  spongy..  . 
crystalline  
Iron,  pure 

253-84 

0.0323 
0.1162 
0.1130 
0.1066 

wrought 

82.92 

steel 

gray  pig  
white  pig  

o  .  1050 

Krypton,  gas  
liquid 

38.5 

22.6 
I8.3 
13.00 
I4.I 

7-4 
14.8 

9-3 

20.7 

0.04485 
0.0310 
0.8366 
0.2456 
0.1217 
0.03346 
0.0659 

Lanthanum 

Lead 

Lithium 

Magnesium  
Manganese  
Mercury 

2OO.6 

Molybdenum  
Neodymium  

Neon 



Nickel 

6-7 

17.4 
8-5 

0.1084 
0.2438 

Nitrogen,  gas  
liquid 

28.02 
32.00 

32.00 
48.00 

Osmium 

0.03113  ' 
0.2175 

Oxvfren   £?as 

liquid  
Ozone  
Palladium  
Phosphorus,  yel.  .  . 
red.  .  .  .s.  

14-3 

9.2 
17.0 

13  'I 
17.6 

9.2 
44-7 

21.8 

0.0592 

O.2O2 

0.1829 

0.0323 
0.1729 

124.16 
124.16 

liquid   . 

Platinum  

Potassium  

Praseodymium.  .  .  . 
Radium 

Rhodium  

8-5 
55-78 

0.05803 
O.O8O2 

Rubidium 

PHYSICAL   CONSTANTS  OF  THE  ELEMENTS 


451 


OF  THE  ELEMENTS 


1 

z 

|j^ 

.J  •  "rt 

<&x 

Electrical 
conduc- 
tivityf 
at  o°  C. 

Thermal 
conductivity 
K*  at  o°  C. 
Ag=i.oo 

Linear  coefficient  of 
expansion 

Melting 
point, 

Boiling 
point, 

I 

2 

3 
4 

6 

8 
9 

10 

ii 

12 
13 

14 

15 

16 

17 

18 

19 

20 
21 
22 

23 
24 

25 
26 
27 
28 
29 
30 
31 
32 

33 
34 
35 
36 
37 
38 
39 
40 

3-44 
6.05 

6.56 
4.27 
6.16 

.033270 

At  °  C. 

-259° 

-252.5° 

119500 

.04417 

40° 

155° 

700° 

.04837 

-190-17 

114.2° 
2250° 
1950° 
I5300 
1600° 

1375° 

1275°. 
1075 

-169° 

184-35° 

6.23 
6.50 
6.32 
5.96 

5  '-87 

131000 

63000 
f  10200- 
\II300 

040700 
O4Il82 
04!! 
04!  I 
o4io6i 

.042924 
.o46oo 
.042694 

40° 
o°-ioo° 
o°-ioo° 
o°-ioo° 

40° 

.1665 

.2070 
.1300 

.1490 

•0836" 

2450° 
-151-7° 

'40°" 

o°-i8o° 
40° 

'o°-ioo°' 

6.23 

3-52 
5-86 
5-98 
6.70 
6.69 
6-33 

810° 

327° 
186° 
650° 
1260° 
-38.85° 
2500° 
840° 

-253° 

1452°     o 
—  210.5 

1525°  
>I400° 

1120° 

1900° 

357-33° 

-243° 
-195-5° 

50400 
II9OOO 
230000 

10630 

.3760 

.0148 

.1420 

.04524 

.03182 
.041279 

6.36 
3-42 

5-95 
3.48 

6'.32 
6.26 
5.67 

I442OO 

40° 
"40°" 

"40°" 
o°-44° 

105300 

.040657 

.041176 
.03124 

2700° 
-227° 

•04563 
".1683" 

-182.7° 

97900 

decomp.  270° 
1550° 
44-1° 
725° 

-119° 

290° 

350°  (yel.) 

.1664 

6.29 
6.51 

9I2OO 
150500 

.040899 
.0483 

40° 
o°-5o° 

"40°" 

1753° 
63-5° 
940° 
700° 
1970° 
39° 

757-5° 

5-97 

.040850 

696° 

452 


APPENDIX 


PHYSICAL  CONSTANTS 


1 

£ 

Name 

Sym- 
bol 

Atomic 
weight. 
0  =  i6 

Molec- 
ular 
weight 

Specific  Gravity. 
Water=i. 
Air=i  (A). 
Hydrogen=i  (D). 

Atomic 
vol. 
At.  wt. 

Specific 
heat 
ato°C. 

Sp.  Gr. 

I 

2 

3 
4 

1 

S 
9 

10 

ii 

12 
13 

14 
15 

16 

17 

1  8 

!Q 
20 
21 

22 

23 
24 

25 
26 

27 
28 
2Q 
30 
31 

3-1 
33 

34 

35 
36 

H 

39 
40 

Ruthenium,  spon.  . 
melted 

Ru 
Ru 
Ru 

Sm 
Sc 
Se 
Se 
Se 
Si 
Si 
Ag 
Na 
Sr 

S 
S 
Sa 
S/3 
ST 
Ta 
Te 
Te 
Tb 
Tl 
Th 
Th 
Tm 
Sn 
Sn 
Sn 
Ti 
W 
U 
V 

Xe 

Xe 
Yb 
Yt 
Zn 
Zr 
Zr 

101  .7 
101  .7 

IOI.7 
I50-4 

44.1 
79-2 
79-2 
79-2 
28.3 
28.3 
107.88 
23.00 
87-63 

32.06 
32.06 
32.06 
32.06 
32.06 
181.5 
127-5 
127.5 
159-2 
204.0 
232.40 
232.40 
168.5 
118.7 
118.7 
118.7 
48.1 
184.0 
238.2 
51.0 

130.2 
130.2 

173-5 
88.7 
65.37 
90.6 
90.6 

:::::: 

8.6 
II.4 

12.268° 
7-7-7.8 

4.  26^-4'.  2825°    ' 

4-4725° 
4.826° 

2.00 
2.491°° 

JO-53 
O.97I2200 

2-54 

1-9556°° 
2.046 
2.05-2.07°° 
1.958 
1.92 

14.49**° 
6.ois20° 
6.27 

II.  8 
8.9 

8-3 
19.4 

cry  st. 

0.0611 

Samarium  
Scandium  
Selenium,  amorph. 
monoclinic  
hexagonal 

633-6 
633-6 
633-6 

18.5 
17.7 

I6.5 
14.2 
11.4 
IO.2 
23.6 
34-5 

I6.4 
15-6 
15-6 
16.4 
l6.7 

12-5 
21  .2 
2O.4 

0.09533 

o  .  08401 

Silicon,  amorph.  .  . 
cryst 

0.2421° 

o.i69722° 
0.0559 
0.2813 

Silver 



Sodium 

Strontium 

256.48 
256.48 
256.48 
256.48 
256.48 

Sulphur, 
amorphous  soft, 
yellow 
rhombic  . 

0.1728 
0.1809 
0.1902 
0.03017 
0.0525 
0.0475 

monoclinic  
plastic  

Tantalum  
Tellurium,  amorph 
cryst  
Terbium 

255-0 

255-0 

Thallium 

11.85 
n.ooH0 
11.23 

17.2 
21.  1 

20.7 

0.0326 

Thorium,  amorph. 
cryst 

Thulium 

Tin,  gray  
rhombic  
tetragonal 

5.8466160 
6.53-6.56 
7.2984150 
4-5017-50 
18.77 
18.685^° 

6.025H° 
f4.22  A.I 

163.5D./ 
3.52-100.10 

20.3 

18.2 

I6.3 
10.7 
9-8 
12.8 

8-5 
37-o 

0.0545 
0-0559 
0.0559 
0.1125 
0.0336 
0.0280 
o  .  i  240 



Titanium 

Tungsten 

Uranium 

Vanadium  
Xenon,  gas  

liquid  
Ytterbium 

65-37 

Yttrium  

3.8o15° 
7.I42160 

4-15 
6.4o18° 

23-4 

9-2 
21.8 

14.2 

0.09356 

Zinc 

Zirconium,  amorph 
cryst 

0.0660 

PHYSICAL   CONSTANTS  OF  THE   ELEMENTS 


453 


OF  THE  ELEMENTS 


Number  || 

jjlj 

<8<x 

Electrical 
conduc- 
tivityt 
at  o°  C. 

Thermal 
conductivity 
K*  at  o°  C. 
Ag=i.oo 

Linear  coefficient  of 
expansion 

Melting 
point, 
^C. 

Boiling 
point. 

i 

2 

3 
4 
5 
6 

7 
8 

9 

10 

ii 

12 

13 

14 
15 

16 
i? 

18 

iQ 

20 
21 
22 

23 
24 
2^ 
26 
27 
28 
2Q 
30 
31 
32 

33 

34 

35 
36 

38 

39 
40 

At0  C. 

>i95o0 

2000° 
2000° 
1350° 
I2OO° 

50°  (softens) 
I7o°-i8o° 
217° 



6.21 

040963 

40° 



40°" 

7-55 
6.65 

690° 
690° 
690° 
350o; 
35oo 
1955 
877.S0 

.043680 

6.06 
4.82 
6.04 
6.47 

5-54 
5-80 
6.10 
5-46 
6.69 
6.07 

200-15600 
681200 
2IIOOO 
40300 

1  .000 
.365 

.040763 
.041921 
.0472 

•047433 
.046413 

40° 
40° 
o°-5o° 

'i3°:5o°' 
40° 

1420° 

961.5° 
97-6° 
900° 

>I20° 

ignition  pt.  255 

114.  5°o 
119.25 

444-6° 
444.6° 
444-6° 
444.6° 
444-6° 

I3900" 
1390° 

60600 
46600 

.o4o8 
.041675 
.043440 

.043021 

40°" 

0°-20° 

"40°" 

2900° 
446° 
452° 

6.65 

56800 

302° 
>i7oo° 

1280° 

6.49 
6.65 
6.65 
5-4i 
6.18 
6.68 
5-90 

6.12 

5  '-98 

.1528 

stable  <20° 
stable  >i7o° 
232° 
1795° 
3267° 
800° 
1720° 

-140° 

>2275°" 

1450-1600 

76600 

.042234 

'40°" 

—  109.1° 

186000 

•2653 

!800° 

1250° 
419° 

1500° 

2350° 

918° 

.042918 

40° 

454 


APPENDIX 


VAPOR  PRESSURE  OF  WATER 
ACCORDING  TO  REGNAULT 


°c. 

op 

Inches  of 
mercury 

Pounds 
per  square 
inch 

°C. 

o  p^ 

Inches  of 
mercury 

Pounds 
per  square 
inch 

o 

32.0 

0.181 

O  .  0890 

42 

107.6 

2.404 

1  .2l6 

i 

33-8 

0.194 

0-0955 

43 

109.4 

2-533 

-244 

2 

35-6 

0.209 

0.1025 

44 

III.  2 

2.669 

.312 

3 

.  37-4 

0.224 

O.IIOO 

45 

II3.0 

2.811 

-381 

4 

39-2 

0.240 

0.1180 

46 

II4.8 

2-959 

-454 

5 

41  .0 

0.257 

0.1263 

47 

116.6 

3-II4 

•530 

6 

42.8 

0.276 

0.1354 

48 

118.4 

3.276 

.609 

7 

44-6 

0.295 

0.1452 

49 

1  2O.  2 

3-444 

.692 

8 

46.4 

0.316 

0.1551 

50 

122  .O 

3-62 

-78 

9 

48.2 

0.338 

0.1657 

Si 

123.8 

3-8i 

1-87 

10 

50.0 

0.361 

0.1773 

52 

125.6 

4.00 

i  .96 

ii 

51-8 

0.386 

0.1893 

53 

127.4 

4.20 

2.06 

12 

53-6 

0.412 

0.2023 

54 

129.2 

4.41 

2.17 

13 

55-4 

0-439 

0.2158 

55 

I3I.O 

4-63 

2.27 

14 

57-2 

0.469 

o  .  2303 

56 

132.8 

4-85 

2-39 

15 

59-o 

0.500 

0.2456 

57 

134-6 

5-09 

2.50 

16 

60.8 

0-533 

0.2618 

58 

136.4 

5-33 

2.62 

i? 

62.6 

0.568 

0.2789 

59 

138.2 

5-59 

2-75 

18 

64.4 

0.605 

0.2970 

60 

I4O.O 

5-86 

2.88 

iQ 

66.2 

0.644 

0.3162 

61 

I4I.8 

6.14 

3-oi 

20 

68.0 

0-685 

0.3363 

62 

143-6 

6.42 

3-i6 

21 

69.8 

0.728 

0-3577 

63 

145-4 

6.72 

3-30 

22 

71.6 

0-774 

0.3802 

64 

147.2 

7.04 

3-46 

23 

73-4 

0.822 

0.4040 

65 

149.0 

7.36 

3-62 

24 

75-2 

0.873 

0.4289 

66 

150.8 

7-70 

3.78 

25 

77.0 

0.927 

0-4554 

67 

152  .6 

8.05 

3-95 

26 

78.8 

0.984 

0.4833 

68 

154-4 

8.41 

4-13 

27 

80.6 

.044 

0.5126 

69 

156.2 

8-79 

4-32 

28 

82.4 

.106 

0-5434 

70 

158.0 

9.18 

4-51 

29 

84.2 

.172 

0-5759 

7i 

159.8 

9-58 

4-71 

30 

86.0 

.242 

0.6101 

72 

161.6 

IO.OO 

4.91 

31 

87.8 

•315 

0.6461 

73 

163.4 

10.44 

5-12 

32 

89.6 

•392 

0.6838 

74 

165  .2 

10.89 

5-35 

33 

91.4 

•473 

0.7234 

75 

167  .O 

11.36 

5.58 

34 

93-2 

-558 

0.7655 

76 

168.8 

11.84 

5-82 

35 

95-0 

•647 

0.810 

77 

170.6 

12-35 

6.06 

36 

96.8 

.740 

0-855 

78 

172.4 

12.87 

6.32 

37 

98.6 

.838 

0.903 

79 

174.2 

13-40 

6.58 

38 

100.4 

1.941 

0-954 

80 

176.0 

13.96 

6.85 

39 

IO2  .2 

2.049 

i  .007 

81 

177.8 

14-54 

7-14 

40 

IO4.O 

2  .162 

i  .061 

82 

179.6 

I5-I4 

7-44 

4i 

105.8 

2.280 

I  .121 

83 

181.4 

15-75 

7-74 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the  permis- 
sion of  the  editor  and  publishers. 


VAPOR  PRESSURE  OF  WATER 


455 


VAPOR   PRESSURE  OF  WATER   (Continued) 


°c. 

°F. 

Inches  of 
mercury 

Pounds 
per  square 
inch 

c. 

0  Jj^ 

Atmos- 
pheres 

Pounds 
per  square 
inch 

84 

183.2 

16.39 

8.05 

129 

264.2 

2.592 

38.11 

85 

185.0 

I7-05 

8-37 

130 

266.0 

2.671 

39-26 

86 

186.8 

17-73 

8.7I 

131 

267.8 

2-753 

40.47 

8? 

188.6 

18.43 

9-05 

132 

269.6 

2.836 

41.68 

88 

190.4 

19.16 

9.41 

133 

271.4 

2  .921 

42.93 

89 

192  .2 

19.91 

9.78 

134 

273-2 

3.008 

44-21 

90 

194.0 

20.69 

10.16 

135 

275.0 

3-097 

45-52 

Qi 

I9S.8 

21.49 

10.56 

136 

276.8 

3-188 

46.87 

92 

197.6 

22.31 

iQ-95 

137 

278.6 

3.282 

48.24 

93 

199.4 

23.17 

11.38 

138 

280.4 

3-378 

49-65 

94 

2OI  .2 

24.04 

n.  81 

139 

282.2 

3-476 

51.06 

95 

203.0 

24-95 

12  .26 

140 

284.0 

3-576 

52.55 

96 

204.8 

25.89 

12.71 

141 

285.8 

3.678 

54-07 

97 

206.6 

26.85 

I3-I9 

142 

287.6 

3-783 

55-6o 

98 

208.4 

27-85 

13-68 

143 

289.4 

3-890 

57-i6 

99 

2IO.2 

28.87 

14.18 

144 

291  .2 

4.OOO 

58.79 

IOO 

212  .O 

/  29-92 

1           .000* 

14.70 

145 

146 

293.0 
294.8 

4-H3 
4.227 

60.44 
62.13 

IOI 

213.8 

.036* 

I5-23 

147 

296.6 

4-344 

63.86 

102 

215.6 

.074* 

15-79 

148 

298.4 

4.464 

65.62 

103 

217.4 

.112* 

16.35 

149 

300.2 

4-587 

67.41 

104 

219.2 

-152* 

16.94 

150 

302.0 

4.712 

69.26 

105 

221  .0 

•193* 

17-53 

151 

303.8 

4.840 

71.14 

106 

222.8 

-235* 

18.15 

152 

305.6 

4.971 

73.06 

107 

224.6 

.278* 

18.78. 

153 

307.4 

5-104 

75-02 

1  08 

226.4 

I  .322* 

19.44 

154 

309.2 

5.240 

77-03 

109 

228.2 

1.368* 

20.  1  1 

155 

311  .0 

5.38o 

79.07 

no 

230.0 

I.4I5* 

20.80 

156 

312.8 

5-522 

81.22 

III 

231.8 

1.463* 

21.51 

157 

314.6 

5.667 

83.29 

112 

233-6 

I-5I3* 

22  .24 

158 

3l6.4 

5-8i5 

85.47 

"3 

235-4 

1.564* 

22.99 

J59 

318.2 

5-966 

87.69 

114 

237-2 

1.616* 

23.76 

1  60 

320.0 

6.  1  20 

89.96 

115 

239.0 

1.670* 

24-55 

161 

321.8 

6.278 

92.27 

116 

240.8 

1.726* 

25-73 

162 

323.6 

6-439 

94-63 

117 

242.6 

1.782* 

26.2O 

163 

325.4 

6.603 

97.04 

118 

244.4 

1.841* 

27.06 

164 

327.2 

6.770 

99-50 

119 

246.2 

1.901* 

27-94 

165 

329.0 

6.940 

IO2  .OI 

•120 

248.0 

1.962* 

28.85 

1  66 

330.8 

7.114 

104.56 

121 

249.8 

2  .025* 

29.78 

167 

332.6 

7.291 

I07.I8 

122 

251.6 

2  .091* 

30.73 

1  68 

334-4 

7.472 

109.84 

123 

253-4 

2.157* 

31.70 

169 

336.2 

7.656 

112.53 

124 

255-2 

2.225* 

32.70 

170 

338.0 

7-844 

115.29 

!25 

257.0 

2.295* 

33-72 

171 

339-8 

8.036 

n8.ii 

126 

258.8 

2.366* 

34-78 

172 

341.6 

8.231 

120.98 

127 

260.6 

2.430* 

35-86 

i73 

343-4 

8.430 

123.90 

128 

262.4 

2.515* 

36.97 

i74 

345-2 

8.632 

126.87 

Atmospheres. 


456 


APPENDIX 


VAPOR  PRESSURE  OF  WATER   (Continued) 


°c. 

°F. 

Atmos- 
pheres 

Pounds 
per  square 
inch 

°C. 

°P. 

Atmos- 
pheres 

Pounds 
per  square 
inch 

175 

347-0 

8.839 

129.91 

203 

397-4 

16.364 

240.54 

176 

348.8 

9.049 

133.00 

204 

399-2 

16.703 

245-49 

177 

350-6 

9.263 

136.15 

205 

401  .0 

17.047 

250.53 

178 

352.4 

9.481 

139-35 

206 

402  .8 

17.396 

255-67 

179 

354-2 

9-703 

142  .62 

207 

404.6 

I7-75I 

260.88 

1  80 

356.0 

9-929 

145-93 

208 

406.4 

l8.II! 

266.18 

181 

357-8 

10.150 

I49-32 

209 

408.2 

18.477 

27L55 

182 

359-6 

10.394 

J52-77 

210 

410.0 

18.848 

277.01 

183 

361-4 

10.633 

156-32 

211 

411.8 

19.226 

282.58 

184 

363-2 

10.876 

I59-84 

212 

4I3-6 

19.608 

288.21 

185 

365-0 

11.123 

163-47 

213 

4I5-4 

19.997 

293.92 

186 

366.8 

n-374 

167.17 

214 

417.2 

20.391 

299.72 

187 

368.6 

ii  .630 

170.94 

215 

419.0 

20.791 

305.57 

1  88 

370.4 

11.885 

174.76 

216 

420.8 

21.197 

311-57 

189 

372-2 

12.155 

178.65 

217 

422  .6 

21  .690 

317.62 

190 

374-0 

12.425 

182.61 

218 

424-4 

22.027 

323.78 

191 

375-8 

12.699 

186.63 

2I9 

426.2 

22.452 

330.01 

192 

377-6 

12.977 

190.72 

220 

428.0 

22.882 

336.30 

iQ3 

379-4 

13.261 

194.88 

221 

429.8 

23-3I9 

342.70 

194 

381.2 

13-549 

I99.I3 

222 

43i-6 

23.761 

349-21 

iQS 

383-0 

13.842 

203.43 

223 

433-4 

24.2IO 

355-81 

196 

384.8 

14.139 

207  .81 

224 

435-2 

24.666 

362.50 

197 

386.6 

14.441 

212.25 

225 

437-o 

25.128 

369  •  29 

198 

388.4 

14  •  749 

216.77 

226 

438.8 

25-596 

376.17 

199 

390-2 

15.062 

221.37 

227 

440.6 

26.071 

383-15 

200 

392.0 

15-380 

226.04 

228 

442.4 

26.552 

390.22 

2OI 

393-8 

15-703 

230.79 

229 

444-2 

27.040 

397-40 

2O2 

395-6 

16.031 

235-61 

SODIUM  CHLORIDE  SOLUTION  AT  15' 
GERLACH 


Specific 
Gravity 

Per 
cent 
NaCl 

Specific 
Gravity| 

Per 
cent 
NaCl 

Specific 
Gravity 

Per 
cent 

NaCl 

Specific 
Gravity 

Per 
cent 
NaCl 

.00725 

I 

-05851 

8 

.11146 

15 

•16755 

22 

.01450 

2 

-06593 

9 

.11938 

16 

.17580 

23 

.02174 

3 

•07335 

IO 

.12730 

17 

.18404 

24 

.02899 

4 

.08097 

ii 

•13523 

18 

.19228 

25 

.03624 

5 

-08859 

12 

•I43I5 

19 

.20098 

26 

.04366 

6 

.09622 

13 

.15107 

20 

•  20433 

26.395 

.05108 

7 

.10384 

14 

•I593I 

21 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the  permis- 
son  of  the  editor  and  publisher. 


SODIUM   CARBONATE  SOLUTION  AT 


457 


SODIUM  CARBONATE  SOLUTION  AT  15° 
LUNGE 


Specific 
Gravity 

Degrees 
Baume 

Per  cent 
NajCOj 

Per  cent 
Na2CO3.io  H2O 

i  liter  contains  grams 

Na,CO3. 

Na2CO3.io  H2O 

.007 

1  .0 

0.67 

1.807 

6.8 

18.2 

.014 

2.O 

1-33 

3-S87 

13-5 

36.4 

.022 

3-1 

2.09 

5-637 

21.4 

57-6 

.029 

4.1 

2.76 

7-444 

28.4 

76.6 

.036 

5-i 

3-43 

9-25I 

35-5 

95-8 

•045 

6.2 

4.29 

11.570 

44-8 

120.9 

.052 

7.2 

4-94 

i3-323 

52.0 

140.2 

.060 

8.2 

S-7i 

15.400 

60.5 

163.2 

.067 

9- 

6-37 

17.180 

68.0 

183-3 

•075 

10. 

7.12 

19.203 

76.5 

206.4 

.083 

ii  . 

7.88 

21  .252 

85.3 

230.2 

.091 

12. 

8.62 

23  .  248 

94.0 

253-6 

.100 

13- 

9-43 

25.432 

103.7 

279.8 

.108 

14- 

10.19 

27.482 

112.9 

304-5 

.116 

15- 

io-95 

29-532 

122.2 

329-6 

•I25 

16. 

ii.  81 

31.851 

132.9 

358.3 

•134 

17- 

12.61 

34.009 

143-0 

385-7 

.142 

18.0 

13.16 

35-493 

150.3 

405-3 

.152 

19.1 

14.24 

38.405 

164.1 

442.4 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the  permis- 
sion of  the  editor  and  publishers. 


458 


APPENDIX 


CONCENTRATED  SODIUM  CARBONATE  SOLUTION  AT  30* 

LUNGE 


I  liter  contains  grams 

Specific 
Gravity 

Degrees 
Baum6 

Per  cent 
NajCOs 

Per  cent 
Na2CO3.io  H2O 

Na2C03 

NazCOj.io  H2O 

.142 

18.0 

13-79 

37-21 

157-5 

425.0 

.152 

I9.I 

14.64 

39-51 

168.7 

455-2 

.162 

2O.  2 

15-49 

41-79 

180.0 

485-7 

.171 

21-2 

16.27 

43.89 

190.5 

514.0 

.180 

22.1 

17.04 

45-97 

2OI  .1 

542.6 

.190 

23.1 

17.90 

48-31 

2I4.O 

577-5 

.200 

24.2 

18.76 

50.62 

225.1 

607.4 

.210 

25.2 

19.61 

52-91 

237-3 

640.3 

.220 

26.1 

20.47 

55-29 

249.7 

673.8 

.231 

27.2 

21.42 

57.8o 

263.7 

7II-5 

.241 

28.2 

22.29 

60.15 

276.6 

746.3 

.252 

29.2 

23.25 

62.73 

29I.I 

785-4 

•263 

30.2 

24.18 

65.24 

305-4 

824.1 

.274 

31.2 

25.11 

67.76 

3I9-9 

863.2 

•285 

32.2 

26.04 

70.28 

334-6 

902.8 

•2Q7 

33-2 

27.06 

73.02 

35i-o 

947.1 

.308 

34-i 

27.97 

75-48 

365-9 

987.4 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue,  1918,  with  the  permis- 
sion of  the  editor  and  publishers. 

BAUME  AND  SPECIFIC  GRAVITY 


459 


EQUIVALENT   OF   DEGREES   BAUME    (AMERICAN    STANDARD) 
AND  SPECIFIC  GRAVITY  AT  60°  F. 


Degrees  Baume"  =  145  — 


for  Liquids  Heavier  than  Water 


Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

o.o 

1  .0000 

•  7 

I  .0262 

•4 

.0538 

.1 

.0829 

.1 

.0007 

.8 

I  .0269 

•  5 

.0545 

.2 

.0837 

.2 

.0014 

•9 

1.0276 

.6 

•0553 

•3 

.0845 

•  3 

.0021 

4.0 

I  .0284 

•7 

.0561 

•  4 

•0853 

•4 

.0028 

.1 

I  .0291 

.8 

.0569 

•  5 

.0861 

•5 

•0035 

.2 

I  .0298 

•9 

.0576 

.6 

4      .0870 

.6 

.OO42 

•3 

1.0306 

8.0 

.0584 

•7 

.0878 

•  7 

.0049 

•4 

1-0313 

.1 

.0592 

.8 

.0886 

.8 

0055 

•5 

I  .0320 

.2 

•0599 

•9 

.0894 

•9 

.0062 

.6 

I  .0328 

•  3 

.0607 

12.  0 

.0902 

i  .0 

.0069 

•  7 

1-0335 

•4 

.0615 

.1 

.0910 

.1 

.0076 

.8 

1.0342 

•  5 

.0623 

.2 

.0919 

.2 

.0083 

•9 

1-0350 

.6 

.0630 

•3 

.0927 

•3 

.0090 

S-o 

1-0357 

•  7 

•0638 

•  4 

•0935 

•4 

.0097 

.1 

1.0365 

.8 

.0646 

•5 

•0943 

•  5 

.0105 

.2 

1.0372 

•9 

•0654 

.6 

.0952 

.6 

.OII2 

•3 

I  .0379 

9-o 

.0662 

•  7 

.0960 

•  7 

.0119 

•4 

I  .0387 

.1 

.0670 

.8 

.0968 

.8 

.OI26 

•  5 

i  -0394 

.2 

.0677 

•9 

.0977 

•9 

•0133 

.6 

I  .0402 

•3 

.0685 

13.0 

.0985 

2.0 

.OI4O 

•  7 

I  .0409 

•4 

.0693 

.1 

•0993 

.1 

.0147 

.8 

1.0417 

•  5 

.0701 

.2 

.1002 

.2 

.0154 

•9 

I  .0424 

.6 

.0709 

•3 

.IOIO 

•3 

.Ol6l 

6.0 

1.0432 

•  7 

.0717 

•4 

.1018 

•  4 

.0168 

.1 

1-0439 

.8 

.0725 

•  5 

.1027 

•5 

•0175 

.2 

1.0447 

•9 

•0733 

.6 

.1035 

.6 

.0183 

•3 

1-0454 

10.  0 

.0741 

•  7 

•  1043 

•7 

.0190 

•4 

I  .0462 

.1 

.0749 

.8 

.1052 

.8 

.0197 

•  5 

I  .0469 

.2 

•0757 

•9 

.1060 

•9 

.O2O4 

.6 

I  .0477 

•3 

.0765 

14.0 

.1069 

3-o 

.O2II 

•  7 

1.0484 

•4 

•0773 

.1 

.1077 

.1 

.0218 

.8 

I  .0492 

•  5 

.0781 

.2 

.1086 

.2 

.O226 

•9 

I  .0500 

.6 

.0789 

•  3 

.1094 

•3 

•0233 

7.0 

I  .0507 

•  7 

.0797 

•  4 

.1103 

•4 

.0240 

.1 

I.05I5 

.8 

•0805 

•5 

.1111 

•5 

.0247 

.2 

1.0522 

•9 

.0813 

.6 

.II2O 

.6 

•0255 

•3 

i  -0530 

ii  .0 

.0821 

•  7 

.1128 

Reprinted  from  D.  Van  Nostrand's  Chemical  Annual,  Fourth  Issue.  1918.  with  the  permis- 
sion of  the  editor  and  publishers. 


460 


APPENDIX 


EQUIVALENT   OF   DEGREES   BAUMfi    (AMERICAN    STANDARD) 
AND   SPECIFIC  GRAVITY  AT  60°  F.   (Continued) 


Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

.8 

•II37 

.2 

.1526 

.6 

.1944 

28.0 

•2393 

•9 

•II4S 

•3 

•1535 

•  7 

•1954 

.1 

.2404 

15-0 

•II54 

•4 

•1545 

.8 

.1964 

.2 

.2414 

.1 

.1162 

•5 

•1554 

•9 

.1974 

•3 

.2425 

.2 

.1171 

.6 

•1563 

24.0 

.1983 

•4 

.2436 

•3 

.1180 

•7 

•1572 

.1 

•1993 

•5 

.2446 

•4 

.1188 

.8 

.1581 

.2 

.2003 

.6 

•2457 

•  5 

.IIQ7 

•9 

.1591 

•  3 

.2013 

•  7 

.2468 

.6 

.1206 

20.0 

.1600 

•4 

.2023 

.8 

.2478 

•7 

.1214 

.1 

.1609 

•5 

•2033 

•9 

.2489 

.8 

.1223 

.2 

.1619 

.6 

•2043 

29.0 

.2500 

•9 

.1232 

•  3 

.1628 

.7 

•2053 

.1 

.2511 

16.0 

.1240 

•4 

.1637 

.8 

.2063 

.2 

.2522 

.1 

.1249 

•  5 

.1647 

•9 

•2073 

•3 

•2532 

.2 

.1258 

.6 

.1656 

25.0 

.2083 

•4 

•2543 

•3 

.1267 

•  7 

.1665 

.1 

.2093 

•5 

•2554 

•4 

•1275 

.8 

•i67S 

.2 

.2104 

.6 

•2565 

•  5 

.1284 

•9 

.1684 

•3 

.2114 

•  7 

.2576 

.6 

.1293 

21  .O 

.1694 

•  4 

.2124 

.8 

.2587 

•  7 

.1302 

.1 

.1703 

•5 

•2134 

•9 

•2598 

.8 

.1310 

.2 

.1712 

.6 

.2144 

30.0 

.2609 

•9 

•1319 

•  3 

.1722 

•  7 

•2154 

.1 

.2620 

17.0 

.1328 

•4 

•1731 

.8 

.2164 

.2 

.2631 

.1 

•1337 

•  5 

.1741 

•9 

•2175 

•  3 

.2642 

.2 

.1346 

.6 

•1750 

26.0 

.2185 

.4 

•2653 

•3 

•1355 

•  7 

.1760 

.1 

•2195 

•5 

.2664 

•4 

.1364 

.8 

.1769 

.2 

.2205 

.6 

.2675 

•  5 

•1373 

•9 

.1779 

•  3 

.2216 

•  7 

.2686 

.6 

.1381 

22.0 

.1789 

•4 

.2226 

.8 

.2697 

•7 

.1390 

.1 

.1798 

•  5 

.2236 

•9 

.2708 

.8 

•T399 

.2 

.1808 

.6 

.2247 

31.0 

.2719 

•9 

.1408 

•3 

.1817 

•7 

.2257 

.1 

.2730 

18.0 

.1417 

•4 

.1827 

.8 

.  2267 

.2 

.2742 

.1 

.1426 

•  5 

.1837 

•9 

.2278 

•3 

•2753 

.2 

•1435 

.6 

.1846 

27.0 

.2288 

•  4 

.2764 

•3 

.1444 

•  7 

-1856 

.1 

.2299 

•  5 

•2775 

•4 

•1453 

.8 

.1866 

.2 

.2309 

.6 

.2787 

•5 

.1462 

•9 

.1876 

•3 

.2319 

•  7 

.2798 

.6 

.1472 

23.0 

.1885 

•4 

•2330 

.8 

.2809 

•  7 

.1481 

.1 

.1895 

•  5 

.2340 

•9 

.2821 

.8 

.1490 

.2 

•1905 

.6 

•2351 

32.0 

.2832 

•9 

.1499 

•3 

•1915 

•7 

.2361 

.1 

.2843 

19.0 

.1508 

•4 

.1924 

.8 

1.2372 

.2 

•2855 

.1 

•1517 

•5 

•1934 

•9 

1-2383 

•3 

.2866 

BAUME  AND   SPECIFIC  GRAVITY 


461 


EQUIVALENT   OF   DEGREES   BAUMfi    (AMERICAN    STANDARD) 
AND   SPECIFIC  GRAVITY  AT  60°  F.    (Continued') 


Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume 

Specific 
Gravity 

Degrees 
Baume' 

Specific 
Gravity 

•4 

.2877 

.8 

•3401 

.2 

1.3969 

.6 

1.4588 

•5 

.2889 

•9 

•3414 

•3 

I-3983 

•  7 

I  .4602 

.6 

.2900 

37-o 

.3426 

•4 

1.3996 

.8 

.4617 

•  7 

.2912 

.1 

.3438 

•  5 

I  .4010 

•9 

-4632 

.8 

.2923 

.2 

•3451 

.6 

I  .4023 

46.0 

.4646 

•9 

•2935 

•  3 

.3463 

•7 

I.4037 

.1 

.4661 

33-o 

.2946 

•  4 

•3476 

.8 

1.4050 

.2 

•4676 

.1 

.2958 

•5 

.3488 

•9 

I  .4064 

•  3 

.4691 

.2 

.2970 

.6 

•3501 

42  .0 

I  .4078 

•4 

.4706 

•3 

.2981 

•  7 

•3514 

.1 

1.4091 

•  5 

-4721 

•4 

•2993 

.8 

•3526 

.2 

I  .4105 

.6 

•4736 

•  5 

.3004 

•9 

•3539 

•3 

I  .4119 

•  7 

•4751 

.6 

.3016 

38.0 

•3551 

•4' 

I  -4133 

.8 

.4766 

•  7 

.3028 

.1 

•3564 

•  5 

I  .4146 

•9 

.4781 

.8 

.3040 

.2 

•3577 

.6 

I  .4160 

47.0 

•4796 

•9 

.3051 

•3 

•3590 

•7 

I  .4174 

.1 

.4811 

34-o 

•3063 

•  4 

.3602 

.8 

I  .4188 

.2 

.4826 

.1 

.3075 

•5 

•3615 

•9 

I  .4202 

•  3 

.4841 

.2 

.3087 

.6 

.3628 

43-o 

I  .4216 

•4 

.4857 

•  3 

.3098 

•  7 

.3641 

.1 

1.4230 

•5 

-4872 

•4 

.3110 

.8 

•3653 

.2 

1.4244 

.6 

•4887 

•5 

.3122 

•9 

.3666 

•3 

1.4258 

•  7 

.4902 

.6 

.3134 

39-0 

•3679 

•4 

1.4272 

.8 

.4918 

.7 

.3146 

.1 

.3692 

•  5 

1.4286 

•9 

•4933 

.8 

.3158 

.2 

•3705 

.6 

1.4300 

48.0 

.4948 

•9 

.3170 

•3 

.37i8 

•  7 

i.43J4 

.1 

•4964 

35-0 

.3182 

•4 

•3731 

.8 

1.4328 

.2 

-4979 

.1 

•3194 

•5 

•3744 

•9 

1-4342 

•3 

4995 

.2 

.3206 

.6 

•3757 

44.0 

1.4356 

•4 

.5010 

•3 

.3218 

•  7 

•3770 

.1 

I-437I 

•  5 

.5026 

•4 

•3230 

.8 

.3783 

.2 

i  -4385 

.6 

.5041 

•  5 

.3242 

•9 

•3796 

•3 

1-4399 

•  7 

•5057 

.6 

•3254 

40.0 

•  3810 

•4 

1.4414 

.8 

•5073 

•  7 

.3266 

.1 

•3823 

•  5 

i  .4428 

•9 

.5088 

.8 

.3278 

.2 

•3836 

.6 

1.4442 

49.0 

.5104 

•9 

.3291 

•3 

•3849 

•  7 

1-4457 

.1 

.5120 

36.0 

•33°3 

•4 

.3862 

.8 

1.4471 

.2 

•5136 

.1 

•3315 

•5 

.3876 

•9 

1.4486 

•  3 

•5i52 

.2 

•3327 

.6 

.3889 

45-0 

1.4500 

•4 

•5*67 

•3 

-3329 

•7 

.3902 

.1 

I.45I5 

•5 

•5183 

•4 

-3352 

.8 

.3916 

.2 

1.4529 

.6 

•5199 

•  5 

•3364 

•9 

1.3929 

•3 

1-4544 

•  7 

•5215 

.6 

•3376 

41  .0 

1.3942 

•4 

1.4558 

.8 

•5231 

•  7 

•3389 

.1 

I.3956 

•5 

1-4573 

•9 

.5247 

462 


APPENDIX 
HYDROCHLORIC  ACID 


Be.0 

Sp.gr. 

Tw.° 

Percent 
HC1 

Be.0 

Sp.gr. 

Tw.  ° 

Percent 
HC1 

Be.0 

Sp.gr. 

Tw.  ° 

Percent 
HC1 

I.OO 

1.0069 

1.38 

1.40 

16.0 

.1240 

24.80 

24-57 

20.8 

•  1675 

33  So 

32.93 

2.00 

1.0140 

2.80 

2.82 

16.1 

.1248 

24.96 

24-73 

20.9 

.1684 

33-68 

33-12 

3-00 

I.O2II 

4.22 

4-25 

16.2 

.1256 

25.12 

24.90 

21.0 

.1694 

33-88 

33-31 

4-00 

1.0284 

5-68 

5-69 

16.3 

.1265 

25.30 

25.06 

21.  1 

.1703 

34.06 

33  50 

S.OO 

1.0357 

7.14 

7-15 

16.4 

.1274 

25.48 

25  23 

21.2 

.1713 

34.26 

33.69 

5.25 

1.0375 

7.50 

7  52 

16.5 

.1283 

25.66 

25-39 

21.3 

.1722 

34-44 

33-88 

S.SO 

I  0394 

7.88 

7-89 

16.6 

.1292 

25.84 

25.56 

21.4 

.1732 

34.64 

34  07 

5-75 

1.0413 

8.26 

8.26 

16.7 

.1301 

26.02 

25.72 

21-5 

.1741 

34-82 

34.26 

6.00 

1.0432 

8.64 

8.64 

16.8 

.1310 

26.20 

25  89 

21.6 

.1751 

35-02 

34-45 

6.25 

1.0450 

9.00 

9.02 

16.9 

.1319 

26.38 

26.05 

21.7 

.1760 

35-20 

34-64 

6.50 

1.0469 

9-38 

9-40 

17.0 

.1328 

26.56 

26.22 

21.8 

.1770 

35-40 

34  83 

6-75 

1.0488 

9.76 

9.78 

17.1 

.1336 

26.72 

26.39 

21.9 

•  1779 

35.58 

35-02 

7.00 

1.0507 

10.14 

10.17 

17.2 

.1345 

26.90 

26.56 

22.0 

.1789 

35.78 

35-21 

7-25 

1.0526 

10.52 

10.55 

17.3 

•  1354 

27.08 

26.73 

22.1 

.1798 

35.96 

35  40 

7-50 

I-  0545 

10.90 

10.94 

17-4 

.1363 

27.26 

26.90 

22.2 

.1808 

36.16 

35-59 

7-75 

1.0564 

11.28 

11.32 

17.5 

.1372 

27-44 

27.07 

22.3 

.1817 

36.34 

35.78 

8.00 

1.0584 

11.68 

11.71 

17.6 

.1381 

27.62 

27.24 

22.4 

.1827 

36.54 

35-97 

8.25 

1.0603 

12.06 

12.09 

17.7 

.1390 

27.80 

27.41 

22.5 

.1836 

36.72 

36.16 

8.50 

1.0623' 

12.46 

12.48 

17.8 

•1399 

27.98 

27.58 

22.6 

.1846 

36.92 

36.35 

8.75 

1.0642 

12.84 

12.87 

17-9 

.1408 

28.16 

27.75 

22.7 

.1856 

37  12 

36.54 

9.00 

1.0662 

13.24 

13.26 

18.0 

.1417 

28.34 

27.92 

22.8 

.1866 

37-32 

36.73 

9-25 

I.  0681 

13.62 

13  65 

18.1 

.1426 

28.52 

28.09 

22.9 

.1875 

37-50 

36.93 

9-50 

1.0701 

14.02 

14.04 

18.2 

•1435 

28.70 

28.26 

23 

.1885 

37.70 

37-14 

9-75 

1.0721 

14.42 

14-43 

18.3 

.1444 

28.88 

28.44 

23 

.1895 

37-90 

37.36 

10.00 

1.0741 

14.82 

14-83 

18.4 

.1453 

29.06 

28.61 

23 

.1904 

38.08 

37-58 

10.25 

1.0761 

15.22 

15  22 

18.5 

.1462 

29.24 

28.78 

23. 

.1914 

38.28 

37.8o 

10.50 

1.0781 

15.62 

15.62 

18.6 

.1471 

2Q.42 

28.95 

23 

.1924 

38.48 

38.03 

10.75 

1.0801 

16.02 

16.01 

18.7 

.1480 

29.60 

29  13 

23 

.1934 

38.68 

38.26 

II.  OO 

1.0821 

16.42 

I6.4I 

18.8 

.1489 

29.78 

29-30 

23- 

.1944 

38.88 

38.49 

11.25 

1.0841 

16.82 

16.81 

18.9 

.1498 

29.96 

29.48 

23.7 

•  1953 

39-o6 

38.72 

11.50 

I.  0861 

17.22 

17.21 

19.0 

.1508 

30.16 

29.65 

23.8 

.1963 

39.26 

38.95 

11-75 

I.  0881 

17.62 

17.61 

I9-I 

.1517 

30.34 

29.83 

23.9 

•  1973 

39.46 

39.18 

12.00 

1.0902 

18.04 

18.01 

19.2 

.1526 

30.52 

30.00 

24.0 

.1983 

39-66 

39-41 

12.25 

1.0922 

18.44 

18.41 

19-3 

.1535 

30.70 

30.18 

24.1 

•1993 

39-86 

39-64 

12.50 

1.0943 

18.86 

18.82 

19.4 

.1544 

30.88 

30.35 

24.2 

.2003 

40.06 

39-86 

12-75 

1.0964 

19.28 

19.22 

19-5 

.1554 

31.08 

30.53 

24  3 

.2013 

40.26 

40.09 

13.00 

1.0985 

19.70 

19-63 

19.6 

-1563 

31  26 

30.71 

24.4 

2023 

40.46 

40.32 

13-25 

I.  1006 

20.  12 

20.04 

19.7 

•  1572 

31  •  44 

30.90 

24.5 

•  2033 

40.66 

40.55 

13  50 

I  .  1027 

20.54 

20  .  45 

19.8 

.1581 

31  62 

31.08 

24.6 

.2043 

40.86 

40.78 

13-75 

I  .  1048 

20.96 

20.86 

19-9 

.1590 

31.80 

31.27 

24.7 

.2053 

41.06 

41.01 

14.00 

I  .  1069 

21.38 

21.27 

20.  o 

.1600 

32.00 

31-45 

24.8 

.2063 

41.26 

41.24 

14-25 

1.1090 

21.80 

21.68 

20.1 

.1609 

32.18 

31-64 

24.9 

.2073 

41.46 

41.48 

14.50 

i.im 

22.22 

22.09 

20.2 

.1619 

32.38 

31  82 

25.0 

.2083 

41.66 

41.72 

14-75 

1.1132 

22.64 

22.50 

20.3 

1628 

32.56 

32.01 

25.1 

•  2093 

41.86 

41-99 

15  00 

I.IIS4 

23.08 

22.92 

20.4 

1637 

32.74 

32.19 

25.2 

.2103 

42.06 

42.30 

15.25 

1.1176 

23  52 

23  33 

20.5 

1647 

32.94 

32.38 

25.3 

.2114 

42.28 

42.64 

15  So 

I.  1197 

23-94 

23.75 

20.6 

1656 

33  12 

32.56 

25.4 

.2124 

42.48 

43-01 

15-75 

I.  1219 

24.38 

24.16 

20.7 

1666 

33  32 

32.75 

25.5 

2134 

42.68 

43-40 

Specific  Gravity  determinations  were  made  at  60°  P.,  compared  with  water  at  60°  F. 
From  the  Specific  Gravities,  the  corresponding  degrees  Baume  were  calculated  by  the  follow- 
ing formula: 

Baume  =  145  -  5^7?- 


Baume  Hydrometers  for  use  with  this  table  must  be  graduated  by  the  above  formula  which 
formula  should  always  be  printed  on  the  scale. 

Atomic  weights  from  F.  W.  Clarke's  table  of  1901.     O  =  16. 


ALLOWANCE  FOR  TEMPERATURE 


10-15°  Be". 
15-22°  Be. 
22-25°  Be. 


1/40°  Be.  or  .0002  Sp.  Gr.  for  i°  F. 
1/30°  Be.  or  .0003  '  "  i°  F. 
1/28°  Be.  or  .00035 '  i°  P. 


AUTHORITY  —  W.  C.  FERGUSON. 

The  above  table  was  prepared  under  the  supervision  of  the  Manufacturing  Chemists  Associa- 
tion of  the  United  States  and  adopted  by  the  Association  as  standard  for  United  States 
practice.  Reprints  of  each  table  may  be  obtained  from  the  Secretary  of  the  Association,  84  State 
St.,  Boston, 


NITRIC  ACID 


463 


NITRIC  ACID 


Be.0 

Sp.  Gr. 

Tw.  ° 

Percent 
HNO3 

Be.0 

Sp.  Gr. 

Tw.  ° 

Percent 
HN03 

Be\  ° 

Sp.  Gr. 

Tw.  ° 

Percent 
HN03 

10.  OO 

.0741 

14.82 

12.86 

23.00 

.1885 

37-70 

30-49 

36.00 

1-3303 

66.06 

52.30 

10.25 

.0761 

15.22 

13.18 

23-25 

.1910 

38.20 

30-86 

36.25 

1.3334 

66.68 

52.81 

10.50 

.0781 

15.62 

13.49 

23.50 

.  T934 

38.68 

31.21 

36.50 

3364 

67.28 

53.32 

10.75 

.0801 

16.02 

I3-8I 

23.75 

•  1959 

39.18 

31-58 

36.75 

3395 

67.90 

53-84 

11.00 

.0821 

16.42 

14.13 

24.00 

.1983 

39-66 

31-94 

37.00 

3426 

68.52 

54.36 

11.25 

.0841 

16.82 

14.44 

24.25 

.2008 

40.16 

32-31 

37-25 

3457 

69.14 

54-89 

11.50 

.0861 

17.22 

14.76 

24.50 

.2033 

40.66 

32.68 

37.50 

3488 

69.76 

55-43 

11.75 

.0881 

17.62 

IS  07 

24-75 

.2058 

41.16 

33-05 

37-75 

3520 

70.40 

55-97 

12.00 

.0902 

18.04 

15-41 

25  oo 

.2083 

41.66 

33-42 

38.00 

•  3551 

71.02 

56.52 

12.25 

.0922 

18.44 

15.72 

25.25 

.2109 

42.18 

33.80 

38.25 

-3583 

71.66 

57-o8 

12.50 

.0943 

18.86 

16.05 

25.50 

.2134 

42.68 

34-17 

38.50 

-3615 

72  30 

57-65 

12.75 

.0964 

19.28 

i6.39 

25  75 

.2160 

43.20 

34.56 

38.75 

-3647 

72-94 

58-23 

13  oo 

.0985 

19.70 

16.72 

26.00 

.2185 

43-70 

34-94 

39.00 

.3679 

73.58 

58.82 

13  25 

.1006 

20.12 

17  05 

26.25 

.2211 

44.22 

35-33 

39-25 

•3712 

74-24 

59-43 

13  50 

.1027 

20.54 

17.38 

26.50 

.2236 

44.72 

35-70 

39.50 

•  3744 

74-88 

60.06 

13-75 

.1048 

20.96 

17.71 

26.75 

.2262 

45-24 

36.09 

39-75 

3777 

75-54 

60.71 

14.00 

.1069 

21  38 

18.04 

27.00 

.2288 

45.76 

36.48 

40.00 

.3810 

76.20 

61.38 

14.25 

.1090 

21.80 

18.37 

27.25 

.2314 

46.28 

36.87 

40.25 

.3843 

76.86 

62.07 

14.50 

.nil 

22.22 

18.70 

27.50 

•2340 

46.80 

37.26 

40.50 

.3876 

77-52 

62.77 

14-75 

.1132 

22.64 

19.02 

27.75 

.2367 

47-34 

37.67 

40.75 

.3909 

78.18 

63.48 

15  OO 

.1154 

23  08 

19-36 

28.00 

•2393 

47.86 

38.06 

41.00 

•  3942 

78'.  84 

64.20 

15  25 

.1176 

23.52 

19.70 

28.25 

.2420 

48.40 

38.46 

41.25 

.3976 

79-52 

64.93 

IS  So 

.1197 

23-94 

20.02 

28.50 

.2446 

48.92- 

38-85 

41.50 

.4010 

80.20 

65-67 

IS  75 

.1219 

24.38 

20.36 

28.75 

-2473 

49.46 

39-25 

41-75 

.4044 

80.88 

66.42 

16.00 

.1240 

24.80 

20.69 

29.00 

.2500 

50.00 

39-66 

42.00 

.4078 

81.56 

67-18 

16.25 

.1262 

25.24 

21.03 

29.25 

.2527 

50-54 

40.06 

42.25 

.4112 

82.24 

67.95 

16.50 

.1284 

25-68 

21.36 

29.50 

•  2554 

51.08 

40.47 

42.50 

.4146 

82.92 

68.73 

16.75 

.1306 

26.12 

2I-7O 

29-75 

.2582 

51-64 

40-89 

42.75 

.4181 

83.62 

69.52 

17.00 

.1328 

26.56 

22.04 

30.00 

-.2609 

52.18 

41.30 

43  .00 

.4216 

84.32 

70-33 

17-25 

.1350 

27.0O 

22-38 

30.25 

.2637 

52-74 

41.72 

43.25 

.4251 

85.02 

71  15 

I7.50 

.1373 

27.46 

22.74 

30.50 

.2664 

53-28 

42.14 

43.5b 

.4286 

85.72 

71.98 

17  75 

•  1395 

27.90 

23.08 

30.75 

.2692 

53-84 

42.58 

43-75 

•  4321 

86.42 

72.82 

18.00 

.1417 

28.34 

23.42 

31.00 

.2719 

54.38 

43.00 

44.00 

•  4356 

87.12 

73.67 

18.25 

.1440 

28.80 

23.77 

31  25 

.2747 

54-94 

43-44 

44.25 

•  4392 

87.84 

74-53 

18.50 

.1462 

29.24 

24.11 

31  So 

.2775 

55.50 

43.89 

44-50 

.4428 

88.56 

75.40 

18.75 

.1485 

29.70 

24.47 

31.75 

.2804 

56.08 

44-34 

44-75 

.4464 

89.28 

76.28 

19.00 

.1508 

30.16 

24.82 

32.00 

.2832 

56.64 

44-78 

45.00 

•  4500 

90.00 

77.17 

19-25 

-I53I 

30.62 

25.18 

32.25 

.2861 

57-22 

45-24 

45.25 

.4536 

90.72 

78.07 

19.50 

•  1554 

31.08 

25  53 

32.50 

.2889 

57.78 

45-68 

45-50 

-4573 

91.46 

79  03 

19-75 

•  1577 

31-54 

25.88 

32.75 

.2918 

58.36 

46.14 

45-75 

.4610 

92.20 

80.04 

20.00 

.1600 

32.OO 

26.24 

33  oo 

.2946 

58.92 

46.58 

46.00 

.4646 

92.92 

81.08 

20.25 

.1624 

32.48 

26.61 

33  25 

.2975 

59.50 

47-04 

46.25 

.4684 

93.68 

82.18 

20.50 

.1647 

32-94 

26.96 

33  50 

.3004 

60,  08 

47-49 

46.50 

•  4721 

94.42 

8.3  33 

20.75 

.1671 

33  42 

27.33 

33-75 

.3034 

60.68 

47-95 

46.75 

.4758 

95.16 

84.48 

21.  OO 

.1694 

33-88 

27.67 

34.00 

.3063 

61.26 

48.42 

47.00 

.4796 

95.92 

85.70 

21.25 

.1718 

34.36 

28.02 

34.25 

-3093 

61.86 

48.90 

47-25 

.4834 

96.68 

86.98 

21.50 

-I74I 

34-82 

28.36 

34-50 

-3122 

62.44 

49-35 

47-50 

.4872 

97-44 

88.32 

21-75 

.1765 

35.30 

28.72 

34-75 

-3I52 

63.04 

49.83 

47-75 

.4910 

98.20 

89.76 

22.00 

.1789 

35.78 

29.07 

35-00 

.  3182 

63.64 

50.32 

48.00 

.4948 

98.96 

91-35 

22.25 
22  .  SO 

.1813 
.1837 

36.26 
36.74 

29-43 
29.78 

35.25 
35-50 

-3212 
.3242 

64.24 

64.84 

50.81 
5I..10 

48.25 
48.50 

.4987 
1.5026 

99-74 
100.52 

93.13 
95.ii 

22.75 

.1861 

37-22 

30.14 

35-75 

-3273 

65.46 

5l.8o 

Specific  Gravity  determinations  were  made  at  60°  P.,  compared  with  water  at  60°  P. 
From  the  Specific  Gravities,  the  corresponding  degrees  Baume  were  calculated  by  the  follow- 
ing formula: 


Baume  Hydrometers  for  use  with  this  table  must  be  graduated  by  the  above  formula,  which 
formula  should  always  be  printed  on  the  scale. 

Atomic  weights  from  P.  W.  Clarke's  table  of  1901.    O  =  16. 

ALLOWANCE  FOR  TEMPERATURE: 


At  io°-2o°  Be.  —  1/30°  Be.  or  .00029  Sp.  Gr.  =  i°  P 

20°-30°  Be.  —  1/23°  Be.  or  .00044  "      "    =  i°  F 

30°-40°  Be.  —  1/20°  Be.  or  .00060  "      "    =  i°  F. 

40°-48.5°  Be.  —  1/17°  Be.  or  .00084  "      "    =  i°  F. 

AUTHORITY  —  W.  C.  FERGUSON. 


The  above  table  was  prepared  under  the  supervision  of  the  Manufacturing  Chemists  Associa- 
tion of  the  United  States  and  adopted  by  the  Association  as  standard  for  United  States  practice. 
Reprints  of  each  table  may  be  obtained  from  the  Secretary  of  the  Association,  84  State  St., 
Boston. 


464 


APPENDIX 


AQUA  AMMONIA 


Be.0 

Sp.  Gr. 

Per  cent 
NH3 

Be.0 

Sp.  Gr. 

Per  cent 
NH3 

Be.0 

Sp.  Gr. 

Per  cent 
NH3 

IO.OO 

I.OOOO 

.00 

16.50 

.9556 

11.18 

23.00 

.9150 

23-52 

10.25 

.9982 

.40 

16.75 

-9540 

11.64 

23  25 

•  9135 

24.01 

10.50 

.9964 

.80 

17.00 

.9524 

12.  IO 

23.50 

.9121 

24.50 

10.75 

•  9947 

1.  21 

17-25 

.9508 

12.56 

23.75 

.9106 

24.99 

11.00 

.9929 

1.62 

17.50 

•  9492 

I3-O2 

24.00 

.9091 

25.48 

11.25 
11.50 

.9912 
.9894 

2.04 

2.46 

17-75 
18.00 

•  9475 
•  9459 

13-49 
13.96 

24.25 
24.50 

.9076 
.9061 

$.% 

II  75 

.9876 

2.88 

18.25 

•  9444 

14-43 

24.75 

.9047 

26.95 

12.  OO 

•  9859 

3-30 

18.50 

.9428 

14.90 

25.00 

•  9032 

27.44 

12.25 
12.50 

.9842 
.9825 

3-73 
4.16 

18.75 
19.00 

.9412 
•9396 

15-37 
15  84 

25.25 
25  50 

.9018 
.9003 

27-93 

28.42 

12-75 

.9807 

4-59 

19-25 

.938o 

16.32 

25.75 

.8989 

28.91 

13.00 

.9790 

5-02 

19.50 

.9365 

16.80 

26.00 

.8974 

29.40 

13.25 

•  9773 

5-45 

19-75 

•  9349 

17.28 

26.25 

.8960 

29.89 

13  5b 

•  9756 

5-88 

20.00 

•  9333 

17.76 

26.50 

.8946 

30.38 

13  75 

-9739 

6.31 

20.25 

.9318 

18.24 

26.75 

•  8931 

30.87 

14.00 

.9722 

6.74 

20.50 

.9302 

18.72 

27.00 

.8917 

31.36 

14  25 

•  9705 

7.17 

20.75 

.9287 

19.20 

27.25 

31-85 

14-50 

.9689 

7.61 

21.  OO 

.9272 

19.68 

27.50 

.8889 

32.34 

14-75 

.9672 

8.05 

21.25 

.9256 

20.16 

27.75 

.8875 

32.83 

15.00 

.9655 

8.49 

2I.5O 

.9241 

20.64 

28.00 

.8861 

33  32 

15.25 

•9639 

8.93 

21.75 

.9226 

21.12 

28.25 

.8847 

33.81 

15.50 

.9622 

9-38 

22.0O 

.9211 

21.  60 

28.50 

•  8833 

34-30 

15  75 

.9605 

9-83 

22.25 

•  9195 

22.O8 

28.75 

.8819 

34-79 

16.00 

.9589 

10.28 

22.50 

.9180 

22.56 

29.00 

.8805 

35-28 

16.25 

•  9573 

10.73 

22.75 

.9165 

23.04 

Specific  Gravity  determinations  were  made  at  60°  F.,  compared  with  water  at  60°  F. 
From  the  Specific  Gravities,  the  corresponding  degrees  Baume  were  calculated  by  the  follow- 
ing formula: 


Baum6  Hydrometers  for  use  with  this  table  must  be  graduated  by  the  above  formula,  which 
formula  should  always  be  printed  on  the  scale. 

Atomic  weights  from  F.  W.  Clarke's  table  of  1901.    O  =  16. 


ALLOWANCE  FOR  TEMPERATURE 

The  coefficient  of  expansion  for  Ammonia  Solutions,  varying  with  the  temperature,  correction 
must  be  applied  according  to  the  following  table: 


Corrections  to  be  added  for  each 
degree  below  60°  F. 

Corrections  to  be  subtracted  for  each  degree 
above  60°  F. 

Degrees 
Baume 

40°  F. 

50°  F. 

70°  F. 

80°  F. 

90°  F. 

100°  F. 

$ 

18° 

20° 
22° 
26° 

.015°  Be". 
.021 
.027 
•033 
.039 
•  053 

.017°  Be. 
.023 
.029 
.036 
.042 
.057 

.020°  Be\ 
.026 
031 
•  037 
.043 
.057 

.022°  Be". 
.028      ' 
•  033 
.038      ' 
-045 
•059 

.024°  Be. 
.030     ' 
.035     ' 
'.040     ' 
•  047     ' 

.026°  Be. 
.032     ' 
•  037     ' 
.042     ' 

AUTHORITY  —  W.  C.  FERGUSON. 

The  above  table  was  prepared  under  the  supervision  of  the  Manufacturing  Chemists  Asso- 
ciation of  the  United  States  and  adopted  by  the  Association  as  standard  for  United  btates 
practice.  Reprints  of  each  table  may  be  obtained  from  the  Secretary  of  the  Association,  84  State 
St.,  Boston. 


SULPHURIC  ACID 


0 

c5 

0_ 

Id 

rC        •        • 

§*^     " 
K* 

d* 

Its 

0_ 

6 

o 

?d 

o^ 

It 

?i 

It 

1 

s 

ci 
C/2 

* 

p-l 

$%& 

£  M  C 

|° 

C  w 

|-a 

IP 

*  N-" 

£ 

B, 

C/3 

* 

13 

|2| 

£ 

Is 

.11 

S 

* 

J    . 

Ft 

0 

I.  0000 

O.O 

o.oo 

62.37 

o.oo 

o.oo 

32.0 

37 

1.3426 

68.5 

43.99 

83.74 

47.20 

39-53 

-60 

I 

1.0069 

1-4 

1.02 

62.80 

1.09 

0.68 

31-2 

3-8 

I  -3551 

71.0 

45.35 

84.52 

48.66 

41-13 

-S3 

2 

I  .  0140 

2.8 

2.08 

63.24 

2.23 

1.41 

30.5 

39 

1.3679 

73.6 

46.72 

85.32 

50-13 

42.77 

-47 

3 

I.02II 

4.2 

3.13 

63.69 

3.36 

2.14 

29.8 

40 

I.38IO 

76.2 

48.10 

86.13 

5l.6i 

44-45 

—41 

4 

1.0284 

57 

4.21 

64.14 

4-52 

2.90 

28.9 

i 

1.3942 

78.8 

49-47 

86.96 

53  08 

46.16 

—35 

5 

1.0357 

7-1 

5.28 

64.60 

5.67 

3.66 

28.1 

.2 

1.4078 

81.6 

50.87 

87.80 

54-58 

47-92 

—31 

6 

I.O432 

8.6 

6-37 

65.06 

6.84 

4-45 

27.2 

43 

I.42I6 

84.3 

52.26 

ss.e? 

56.07 

49.72 

—27 

7 

I.OSO? 

10.  1 

7-45 

65  S3 

7.99 

5-24 

26.3 

44 

1.4356 

87.1 

53-66 

89.54 

57-58 

51.56 

—23 

8 

1.0584 

ii.  7 

8-55 

66.  01 

9.17 

6.06 

25.1 

5 

1  .  4500 

90.0 

55-07 

90.44 

59-09 

53-44 

—20 

9 

1.0662 

13   2 

9-66 

66.50 

10.37 

6.89 

24.0 

46 

.4646 

92.9 

56.48 

91.35 

60.60 

55.36 

—  14 

10 

.0741 

14.8 

10.77 

66.99 

11-56 

7-74 

22.8 

7 

.4796 

95-9 

57.90 

92.28 

62.13 

57-33 

-IS 

n 

.0821 

16.4 

11.89 

67.49 

12.76 

8.61 

21-5 

8 

.4948 

99-0 

59-32 

93.23 

63-65 

59-34 

-18 

12 

.0902 

18.0 

13.01 

68.00 

13.96 

9  49 

20.  0 

0 

.5104 

102.  I 

60.75 

94.20 

65.18 

61.40 

—  22 

13 

.0985 

19.7 

14-13 

68.51 

15.16 

10.39 

18.3 

0 

.  5263 

105-3 

62.18 

05.20 

66.72 

63.52 

-27 

14 

.1069 

21.4 

15  25 

69.04 

16.36 

11.30 

16.6 

I 

.  5426 

08.5 

63.66 

96.21 

68.31 

65.72 

-33 

IS 

-1154 

23   I 

16.38 

69.57 

17  53 

12.23 

14-7 

2 

I  •  5591 

in.  8 

65-13 

97.24 

69-89 

67.96 

-39 

1  6 

.1240 

24.8 

17-53 

70.10 

18.81 

13.19 

12.6 

1 

I  .  5761 

US-  2 

66.63 

98.30 

71-50 

78.28 

-49 

17 

.1328 

26.6 

18.71 

70.65 

20.08 

14.18 

IO.2 

4 

i  •  5934 

118.  7 

68.13 

99.38 

73.li 

72.66 

-59 

18 

.1417 

28.3 

19.89 

71.21 

21.34 

IS  20 

7-7 

s 

I.6III 

122.  2 

69.65 

100.48 

74-74 

75-10 

19 

.1508 

30.2 

21.07 

71.78 

22.61 

16.23 

4.8 

5 

I  .  6292 

125.8 

71.17 

101.61 

76-37 

77.60 

'f       Q 

20 

.I600 

32.0 

22.25 

72.35 

23.87 

17.27 

+  1.6 

7 

1.6477 

129-  5 

72-75 

102.77 

78.07 

80.23 

£ 

21 

.1694 

33-9 

23  43 

72-94 

25.14 

18.34 

-  1.8 

s 

1.6667 

133-  3 

74.36 

103.95 

79-79 

82.95 

PQ  ' 

22 

.1789 

35.8 

24.61 

73-53 

26.41 

19.42 

-  6.0 

9 

l.686o 

137-2 

75-39 

105.16 

81.54 

85-75 

—  7 

23 

.1885 

37-7 

25.81 

74.13 

27.69 

20.53 

—  ii 

K> 

1-7059 

141.  2 

77  67 

106  .  40 

83.35 

88.68 

+12. 

6 

24 

.1983 

39-7 

27.03 

74-74 

29.00 

21.68 

-16 

11 

1  .  7262 

145.2 

79-43 

107  .  66 

85-23 

91.76 

27-3 

25 

.2083 

41.7 

28.28 

75  36 

30.34 

22.87 

—23 

f)2 

1.7470 

149.  A 

81.30 

108.96 

87.24 

9S.o6 

39- 

I 

26 

.2185 

43-7 

29.53 

76.00 

31.69 

24.08 

—30 

63 

1.7683 

153-  7 

83.34 

110.29 

89-43 

98.63 

46. 

I 

27 

.2288 

45.8 

30.79 

76.64 

33  04 

25.32 

-39 

64 

1.7901 

158.0 

85.66 

111.65 

91.92 

102.63 

46. 

4 

28 

.2393 

47-9 

32.05 

77.30 

34-39 

26.58 

-49 

64! 

1-7957 

I59-I 

86.33 

112.  OO 

92.64 

103.75 

43- 

6 

29 

.2500 

So.o 

33  33 

77.96 

35.76 

27.88 

-61 

Hi 

1.8012 

160.2 

87.04 

112.34 

93.40 

104.93 

41. 

I 

30 

.2609 

52.2 

34-63 

78.64 

37-i6 

29.22 

-74 

64] 

I.  8068 

161.4 

87.8 

112.69 

94-23 

106.19 

37- 

9 

31 

.2719 

54-4 

35  93 

79-33 

33.55 

30.58 

-82 

65 

.  8125 

162.5 

88.65 

H3.05 

95.1. 

107.54 

33- 

i 

32 

.2832 

56.6 

37.26 

80.03 

39.98 

32.00 

-96 

fisi 

.8182 

163.6 

89  55 

113.40 

96.10 

108.97 

24 

6 

33 

.2946 

58.9 

38.58 

80.74 

41.40 

33  42 

-97, 

6s  i 

.8239 

164.8 

90.  6c 

113.76 

97-22 

no.  60 

13-4 

34 

.3063 

61.3 

39.02 

81.47 

42.83 

34-90 

-91 

65? 

.8297 

165.9 

91  -8c 

114.12 

98.5 

112.42 

35 

1.3182 

63.6 

41.27 

82.22 

44.28 

36.41 

-81 

66 

-8354 

167.1 

93.19 

114.47 

100.00 

114-47 

-29 

36 

1.3303 

66.1 

42.63 

82.97 

45-74 

37-95 

-70 

Calculated  from  Pickering's  results,  Journal  of  London  Chemical  Society,  vol.  57,  p.  363. 


Approximate  Boiling  Points 
50°  Be.,  295°  F. 
386°  " 


60° 
61° 
62° 
63° 
64° 
65° 


Allowance  for  Temperature 
At  10°  B  .,  .029°  Be.  or  .00023  Sp.  Gr. 


400" 
415°  " 
432°  " 
451°  || 
485°  " 
538°  " 


.036° 
.035° 
-031° 
.028° 
.026° 
.026° 
•0235° 


-00034 
.00039 
.00041 
.00045 
.00053 
.00057 
.00054 


Specific  Gravity  determinations  were  made  at  60°  P.,  compared  with  water  at  60°  F. 
From  the  Specific  Gravities,  the  corresponding  degrees  Baume  were  calculated  by  the  fol- 
lowing formula:  T/1C 

Baume  =  145  -  ^^ 
op.  Ur. 

Baume  Hydrometers  for  use  with  this  table  must  be  graduated  by  the  above  formula,  which 
formula  should  always  be  printed  on  the  scale. 

66°  Baume  =  Sp.  Gr.  1.8354. 
i  cu.  ft.  water  at  60°  F.  weighs  62.37  Ibs.  av. 
Atomic  weights  from  F.  W.  Clarke's  table  of  1901.    O  =  16. 

H2SO4  =  100  per  cent. 
H,SO4  O.  V.  60' 

O. V.  93-19  loo.oo  119.98 

60°  77.67  83.35  100.00 

50°  62.18  66.72  80.06 

Acids  stronger  than  66°  Be.  should  have  their  percentage  compositions  determined  by  chemi- 
cal analysis. 

AUTHORITIES.  —  W.  C.  FERGUSON;  H.  P.  TALBOT. 

_  The  above  table  was  prepared  under  the  supervision  of  the  Manufacturing  Chemists  Asso- 
ciation of  the  United  States  and  adopted  by  the  Association  as  standard  for  United  States 
practice.  Reprints  of  each  table  may  be  obtained  from  the  Secretary  of  the  Association,  84  State 
St.,  Boston. 

(465) 


466 


APPENDIX 


COMPARISON  OP  METRIC  AND  CUSTOMARY  UNITS  FROM  i  TO  9 

i.   LENGTH 


Inches      Millimeters 
(in.)              (mm.) 

Feet          Meters 
(ft.)       •       (m.) 

Yards       Meters 
(yd.)          (m.) 

0.039  37=1 
0.078  74=2 
0.118  n=3 
o.i5748=4 

1=0.304  801 
2=0.609  601 
8=0.914402 
4=1.219202 

1=0.914  402 
2=1.828804 
3=2.743205 
4=3.657607 

0.19685=6 

0.236  22  =  6 

0.27559=7 
0.31496=8 
0.35433=9 

=  1.524003 
=  1.828804 
=2.133604 
=2.438  405 
=2.743205 

6=4.572009 
6=5.486411 
7=6.400813 
8=7.315215 
9=8.229  616 

1=  25.4001 
2=  50.8001 
=  76.2002 
=  101.6002 

3.28083=! 
6.561  67=2 
9.84250=3 
13-12333=4 

1.093611  =  ! 

2.187  222  =  2 

3.280833=3. 

4.374444=4 

=  127.0003 
=  152.4003 
=  177.8004 
=203.2004 
=228.6005 

16.40417= 
19.68500= 
22.96583= 
26  .  246  67  = 
29.52750= 

5.468056=5 
6.561  667=6 
7.655278=7 

8.748889=8 
9.842500=9 

2.  AREA 


Square        Square 
inches     centimeters 
(sq.  in.)         (cm.2) 

Square       Square 
feet          meters 
(sq.  ft.)          (m.2) 

Square        Square 
yards         meters 
(sq.  yd.)          (m.2) 

0.15500=! 
0.31000=2 
0.465  oo=3 
0.62000=4 

1=0.092  90 
2=0.185  81 
8=0.27871 
4=0.371  61 

1=0.8361 
2  =  1.6723 
3=2.5084 
4=3-3445 

0.77500=5 
0.93000=6 
1.08500=7 
1.24000=8 
1-39500=9 

6=0.46452 
6=0-557  42 
7=0.650  3? 
8=0.74323 
9=0.836  13 

6=4.1807 
6=5-0168 
7=5.8529 
8=6.6890 
9  =  7.5252 

1=  6.452 
2=12.903 
3=19-355 

4=25.807 

10.764=1 
21.528=2 
32.292=3 
43-055=4 

1.1960=1 
2.3920=2 
3.588o=3 
4.7839=4 

6=32.258 
6=38.710 
7=45-161 
8=51.613 
9=58.065 

53.819=6 
64.583=6 
75-347=7 
86.111=8 
96.875=9 

5-9799=5 
7-1759=6 
8.3719=7 
9.5679=8 
10.7639=9 

From  Circular  No.  47,  U.  S.  Bureau  of  Standards. 


3.   VOLUME 


Cubic         Cubic 
inches        centi- 
(cu.  in.)      meters 
(cm  .3) 

Cubic        Cubic 
feet          meters 
(cu.  ft.)         (m.») 

Cubic     Cubic 
yards    meters 
(cu.  yd.)  (m.3) 

Cubic 
inches          Liters 
(cu.  in.)          (1.) 

Cubic 
feet          Liters 
(cu.  ft.)          (1.) 

O.O6I  02  =  1 

=0.028  317 

1=0.7646 

1=0.0163867 

1=  28.316 

0.12205=2 

=0.056  634 

2=1.5291 

2=0.032  773  4 

2=  56.633 

0.18307=3 

=0.084951 

8=2.2937 

8=0.049  1602 

3=  84.949 

0.24409=4 

=0.113  268 

4=3.0582 

4=0.065  546  9 

4=113.265 

0.305  12=6 

=0.141585 

6=3.8228 

6=0.0819336 

6  =  141.581 

0.366  14=6 

=0.169902 

6=4.5874 

6=0.098  320  3 

6=169.898 

0.427  i6=7 

=0.198219 

7=5-3519 

7=o.H4  7070 

7  =  198.214 

0.488  19=8 

8=0.226536 

8=6.1165 

8=0.1310938 

8=226.530 

0.54921=9 

9=0.254  853 

9=6.88io 

9=0.147  480  5 

9=254-846 

1  =  16.3872 

35.314=1 

1-3079=1 

61.025=1 

0.035315=! 

2=  32.7743 

70.629=2 

2.6159= 

122.050=2 

0.070  631=2 

3=  49.1615 

105-943=3 

3-9238= 

183.075=8 

0.105946=8 

4=  65.5486 

141.258=4 

5.2318  = 

244.100=4 

0.141  262=4 

5  =  81.9358 

176.572=6 

6.5397  = 

305.125=5 

0.176577=6 

6=  98.3230 

211.887=6 

7.8477  = 

366.150=6 

O.2II  892  =  6 

7=114.7101 

247.201=7 

9.1556=7 

427.175=7 

O.247  2O8=7 

8=131.0973 

282.516=8 

10.4635=8 

488.200=8 

0.282523=8 

9=147.4845 

317.830=9 

11.7715  =  9 

549-225=9 

0.317839=9 

4.   CAPACITY 


LIQUID 

MEASURE 

DRY  MEASURE 

U.  S.         Milli- 
fluid           liters 
ounces 
(fl.  oz.)         (ml.) 

U.S. 
liquid    Liters 
pints 
(pt.)        0.) 

U.S. 
liquid       Liters 
quarts 
(qt.)           (1.) 

U.  S.          Liters 
gallons 
(gal.)             (1.) 

U.S. 
dry        Liters 
quarts 
(qt.)           0.) 

0.033815=! 
0.067629=2 
o.ioi  444=3 
0.135259=4 

1=0.473  17 
2=0.94633 
8  =  1.41950 
4=1.892  67 

1=0.94633 
2  =  1.892  67 
8=2.83900 
4=3.78533 

0.264  i8=l 
0.52836=2 
0-79253=3 
1.056  71=4 

0.9081  =  1 
1.8162=2 
2.7243=3 
3.6324=4 

0.169074=6 
0.202888=6 
0.236703=7 
0.270  518=8 
0.304333=9 

6  =  2.36583 
6=2.83900 
7=3.312  17 
8=3.78533 
9=4.258  50 

6  =  4.73167 
6=5.67800 
7  =  6.62433 
8  =  7.57066 
9=8.51700 

1.32089=6 
1.58507=6 
1.849  24=7 
2.11342=8 
2.37760=9 

4-5405=5 
5.4486=6 
6.3567=7 
7.2648=8 
8.1729=9 

1=  29.573 
2=  59-146 

=  88.719 
=  118.292 

2.1134=1 
4.2268=2 
6.3403=8 
8.4537=4 

1.056  71  =  1 
2.113  42=2 
3.17013=3 
4.22684=4 

1=  3.78533 
2=  7.57066 
8=11.35600 
4=15.14133 

1  =  1.1012 

2  =  2.2024 

3=3  3036 

4=4.4048 

=  147.865 
=  177-437 
=207.010 
8=236.583 
9=266.156 

10.5671  =  6 
12.6805=6 
14.7939=7 
16.9074=8 
19.0208  =  9 

5.28355=5 
6.340  26=6 
7.39697=7 
8.45368=8 
9-51039  =  9 

6  =  18.92666 
6=22.711  99 
7=26.497  33 
8=30.282  66 
9  =  34.06799 

5  =  5.5o6o 
6=6.6072 
7  =  7.7084 
8=8.8096 
9=9.9108 

From  Circular  No.  47,  U.  S.  Bureau  of  Standards. 


(467) 


468 


APPENDIX 

5.  MASS 


Troy 
ounces 

(oz.  t.) 

Grams 
(g.) 

Avoirdu- 
pois          Grams 
ounces 
(oz.  av.)           (g.) 

Avoirdu-       Kilo- 
pois           grams 
pounds 
(Ib.  av.)        (kg.) 

0.032  151  =  1 

0.035274= 

1=0.45359 

0.064  301  = 

0.070548= 

2=0.907  18 

0.096452= 

0.105  822  = 

3=1.36078 

0.128603= 

0.141096= 

4=1.81437 

0.160754= 

0.176370= 

6=2.26796 

0.192  904= 

0.211  644= 

6=2.721  55 

0.225055= 

0.246918= 

7=3.175  15 

0.257  206= 

0.282  192  = 

8=3.62874 

0.289357= 

0.317466= 

8=4.08233 

= 

31-103 

1=  28.350 

2  .  2O4  62    =  1 

= 

62.207 

=  56.699 

4.40924  =2 

= 

93-310 

=  85.049 

6.61387  =3 

=  124.414 

=  113.398 

8.81849  =4 

=  155-517 

=  141.748 

11.023  n=5 

=  186.621 

=  170.097 

13-22773=6 

=217.724 

=  198.447 

15.43236=7 

=248.828 

8  =  226.796 

17.636  98=8 

=279-931 

8=255.146 

19.841  6o=9 

From  Circular  No.  47,  U.  S.  Bureau  of  Standards. 


INDEX 


Abietic  acid,  265 
Absorbency  of  papers,  410 
Acid  colors,  320 

in  paper,  determination  of,  422 
sulphite  cooking  liquor,  160 

effect  on  metals,  178 

strength  of,  176,  184,  190 

systems  of  making,  169 

testing,  209 

thiosulphuric  acid  in,  166 
Acids,  action  on  cellulose,  8 
Adansonia,  40 
Adhesives   for  coating,  328,  331,  333, 

343,  345 
Albumen,  343 

Alcohol  from  soda  cooks,  117 
sulphate  process,  147 
sulphite  process,  198,  205 
Alder,  62 

Alkali  cellulose,  20 
Alum,  269,  277 

amount  necessary  in  sizing  270,  280 

cake,  composition,  278 

composition,  279 

decomposition  by  cellulose,  7 

effect  on  glue,  259 

free  acid  in,  280 

iron  in,  279 

manufacture,  278 

method  of  adding  to  beaters,  281 

substitutes,  269 

testing,  282,  286 

use  in  clarifying  water,  359 
Aluminum  resinate,  269 

sulphate  (table),  444,  445 
Ammonia  (table),  464 
Analyses,  see  Testing 


Aniline  dyes,  313 

absorption  by  fillers,  314 

adding  to  beaters,  317 

classification  of,  317 

dissolving,  317 

mordants  for,  316 
Annatto,  313 
Antichlors,  244 
Antifroth  oils,  329,  349 
Appendix,  444 
Asbestine,  301 

Ash,  determination  in  papers,  414 
in  fibrous  materials,  415 
qualitative  analysis  of,  416 
Ashcroft  tester,  406 
Asparagus  for  pulp,  44 
Aspen,  6 1 

B 

Bache-Wiig  process  for  ground  wood, 

222 

Backwater,  use  in  bleaching,  239 
Bagasse,  43 
Balm  of  Gilead,  61 
Bamboo,  43,  86 

compositon  of,  87 

pectose  in,  93 

treatment  recommended,  87 

yield  of  stems  per  acre,  86 

fibre,  87 
Bark,  55 

in  soda  process,  95 

sulphite  process,  158 
Barker  acid  system,  173 
Barkers,  158 
Barytes,  346 
Basic  colors,  318 
Basswood,  65 


469 


470 


INDEX 


Bast  fibres,  37 

Baume  and  specific  gravity  (table),  459- 

461 

Beating  test  for  wood  pulps,  372 
Beech,  62 

Binder  from  sulphite  waste  liquor,  201 
Birches,  61 
Bisulphites  (see  also  acid),  160 

losses  in  preparing,  176 
Black  ash,  133 

furnaces,  132,  149 
leaching  tanks,  133 
waste,  135 

testing,  140 
Black  gum,  65 
Black  liquor,  123 

composition  of,  123,  127,  147 
evaporation  of,  127 
table,  444 
testing,  139 

use  in  sulphate  process,  142 
utilization  of,  125 
Blanc  fixe,  346 
Bleach  required  by  fibres,  123,  380,  381 

water,  354 

Bleached  pulp,  blueing  of,  253 
color  change  on  storing,  254 
oxycellulose  in,  252 
washing,  246 
Bleaching,  225 
apparatus,  240 

determination  of  degree  ot,  n 
Dobson  process,  242 
effect  of  acid,  240,  242 
temperature,  234 
on  chemical  properties,  251 

strength  of  fibres,  249,  250 
ground  wood,  244 
Hermite  process,  233 
jute,  243 
principles  of,  234 
rate  of  color  change,  239 
systems,  241 
use  of  antichlors,  244 

backwater,  239 
weight  lost  on  bleaching,  236 


Bleaching  with  chlorine  gas,  226 

permanganates,  247 

peroxides,  perborates,  etc.,  249 
Bleaching  powder,  228 

action  on  metals,  231 

deterioration,  229,  231 

dissolving,  230 

sludge  from,  230 

testing,  254 
Blow  pits,  194 

tanks,  118 

Blowing  down  pressure,  193 
Boiler  compounds,  356 

scale,  355 

Boiling  wood  for  grinding,  219 
Bricks  for  digester  linings,  181. 
Bright's   method   for   unbleached   sul- 
phite, 393 
Bulk  of  fibrous  materials,  65 

paper,  determining,  400 
Bulker,  pressure,  401 
Burgess  acid  system,  173 
Bursting  strength  of  paper,  404 


Calcium   hypochlorite,    color   of   solu- 
tions, 232 
solid,  232 

Calender  staining,  321 
Casein,  composition,  334 

detection  in  paper,  418 

deterioration  of,  339 

determination  in  paper,  425 

influence  on  penetration  of  oil,  328 

insoluble  matter  in,  337 

molding  of,  337 

preservation  of  solutions,  338 

properties  and  preparation,  333 

sizing,  286 

soluble,  335 

solvents,  336 

testing,  339 

waterproofing,  338,  339 
Cattle  feed  from  waste  sulphite  liquor. 
203 


INDEX 


471 


Causticity  of  soda  cooking  liquor,  109 
Causticizing  methods,  98 
Cell,  structural  unit  of  plant,  34 
Cellulose,  i 

acetates,  17 

action  of  salts  on,  7 

and  acids,  8 
alkalis,  9,  20 
ferments,  12 
water,  3 

benzoatesr  19 

chlorinated,  251 

commercial  meaning,  2 

composition  and  constitution,  2 

compound,  23 

compounds  of,  13 

copper  number  of,  n,  252 

cuto-,  23 

decomposition  of,  8,  12 

destructive  distillation  of,  13 

determination  of,  27 

esters,  18,  19 

formates,  19 

groups  of,  22 

hydrates,  4 

ligno-,  24,  156 

nitrates,  13 

nitrites,  17 

normal  moisture,  4 

oxidation  of,  10 

pecto-,  23 

peroxide,  n 

physical  properties,  i 

solvents  for,  5 

sulpho-carbonate,  20 

xanthate,  20 

Cement  for  digester  linings,  180 
Chardonnet  silk,  15 
Chestnut,  62 
Chips,  length  of,  159 
Chlorinated  cellulose,  251 
Chlorine  gas,  225 

in  bleached  fibre,  252 

in  paper,  421 

preparation  by  electrolysis,  232 
Chrome  yellow,  310 


Clark  process  for  water  softening,  357 
Clay,  294 

composition  of,  295 

fineness  of  particles,  296 

for  coating,  345 

specific  gravity,  297 

testing,  297,  302 
Coated  paper,  325 

body  stock  for,  326 
brittleness  of,  440 
finish  on,  329 
picking  of,  328 
printing  qualities,  330,  344 
waterproof,  338 
Coating,  coloring  of,  321 

determining  amount  on  paper,  424 

glycerine  in,  329,  349 

method  of  applying,  326 

minerals  used,  328 

oils,  soaps  and  waxes,  329 
Cochineal,  313 
Color  standards  for  bleached  pulp,  379, 

381 

water,  362 
Coloring,  306 

comparing  colors,  307 

matching  shades,  306 

mineral  colors,  308,  310 

mordants,  316 

organic  colors,  313 

pigments,  308 

vulcanized  fibre,  323 
Colors,  acid,  320 

basic,  318 

direct  cotton,  317 

cosines  and  rhodamines,  319 

pigments,  308 

testing,  322 

Combustion  chamber,  166 
Cooking  liquor,  testing,  137,  152,  209 
Cooking  sulphite,  following  progress  in, 

191 
irregularities  in,  191 

Mitscherlich  process,  183 
precautions,  186 
recording  conditions,  187 


472 


INDEX 


Cooking  sulphite,    Ritter-Kellner  pro- 
cess, 184 

schedules  for,  186 
superheated  steam  for,  185 

Coolers  for  sulphur  dioxide,  168 

Copper  number  of  cellulose,  n,  252 

Corn  stalks,  43 

Cotton,  36 

Cotton  stalks,  44 

Cottonwood,  61 

Cucumber  tree,  63 

Cuprammonium  hydrate  cellulose,  5 

Cutch,  313 

Cuto-cellulose,  23 

Cutter     for    sampling     wood     pulps, 

369 

Cutting  press  for  color  disks,  376 
Cymene,  198 


Daylight  lamps,  307,  375,  379 
Decay  of  wood,  56 

effect  on  soda  process,  95 
Defects  in  printing,  435 
Densities  of  soda  stock,  122 
stock  in  bleaching,  234,  241 
sulphite  stock,  195 
Digesters,  soda,  97,  98 
sulphate,  142 
sulphite,  178 
bronze,  179 
Mitscherlich,  183 
Salomon-Brlingger,  179 
sizes  of,  181 

Direct  cotton  colors,  317 
Dirt  in  pulps,  383 
Disk  machine   for   color   comparisons, 

376 
District    of    Columbia    paper    tester, 

405 

Dobson  bleaching  process,  242 
Dolomite  for  acid  making,  174 
Dorr  causticizing  process,  100 
Douglas  spruce,  60 
Drying  sized  papers,  273 
Ducts,  proportion  to  fibres,  392 


E 

Eau  de  Javel,  227 

Electrolyzing  salt,  232 

Electrolytic  bleach,  233 

Electrotypes,  431 

Elements,  table  of  physical  constants, 

448-453 

Enderlein's  evaporator,  128 
Enge  process  for  ground  wood,  223 
Eosines,  319 
Esparto,  42,  77 

alkali  required,  78 

bleaching  fibre  from,  79 

boilers,  78 

bulk  of,  66 

cooking  conditions,  79 

dust,  77 

recovery  of  alkali,  79 
Evaporators,  Enderlein's,  128 

Torion,  127 

Yargan,  128 

Zaremba,  131 


Ferments,  action  on  cellulose,  12 
Fert  ilizer  from  waste  sulphite  liquor,  202 
Fibre  length  of  woods,  49 
Fibres,  estimation  in  paper,  387 

by  method  of  Spence  and  Krauss, 

392 

Fibrous  materials,  bulk  of,  65 
Fillers,  290 

absorption  of  dyes  by,  314 

effect  on  sizing,  290 

•effect  on  strength  of  paper,  290 

losses  in  process,  293 

materials  used,  291 

retention  of,  292,  417 

testing,  302 
Filters,  358 
Firs,  58 

Folding  endurance  of  paper,  406 
Formaldehyde  in  coatings,  338 
Freeman  process  for  soda  cooks,  115 
Fuel  from  waste  sulphite  liquor,  203 


INDEX 


473 


Furfural,  n 

Furnaces,  recovery,  132,  149 

G 

Gas  bleaching,  226 
pressure  in  sulphite  cooks,  188 

relieving,  189 
recovery,  192 
Gelatine,  258 

testing,  261,  332 
Glarimeter,  402 
Gloss  of  paper,  402 
Glue,  258 

detection  of,  419 
determination  of,  425 
for  coating,  331 

sizing,  287 

Glycerine  in  coating,  329,  349 
Grease-proof  qualities  of  paper,  412 
Grinders  for  wood  pulp,  212,  213 
Groundwood  pulp,  212 

Bache-Wiig  process,  222 
bleaching,  224 
condition  of  stone,  216 

wood,  218 

efficiency  of  grinding,  219 
estimation  in  paper,  427 
from  boiled  or  steamed  wood,  219 
in  print  papers,  89 
sand  settlers,  214 
screens  for,  213 
speed  of  stones,  217 
stones  for  making,  212 
temperature  of  grinding,  218 
testing,  223 
woods  for,  221 
Gun-cotton,  15 
Gypsum,  298 

H 

Halftone  plates,  430 

standard  depths,  431 
screens  for  different  papers,  433 
Hardness  in  water,  cause,  353 
determining,  364 
effect  on  sizing,  353 


Heartwood,  49 

Heavy  spar,  301 

Hemlock,  60 

Hemp,  38 

Hermite  electrolytic  bleach  process,  233 

Herreshoff  pyrites  burner,  166 

Herzberg  stain,  389 

Hydrocellulose,  4,  8 

Hydrochloric  acid  (table),  462 

Hypochlorites,  226,  233 

Hypochlorous  acid,  227 


Incinerating  furnaces,  132,  149 
Indanthrenes,  321 
Ingersoll  glarimeter,  402 
Ink,  choice  of,  434 

double  tone,  442 

drying,  438 

for  sizing  test,  413 

mottling  of,  441 

offsetting,  437 


Jute,  39 

bleaching,  243 


Knots,  56,  94,  159 
Kraft  fibre,  141 


Lamp  black,  312 

Larch,  60 

Leaching  tanks  for  black  ash,  133 

Lignin,  25,  35,  157 

reactions  with  sulphurous  acid,  157 

sulphonic  acid,  157 
Ligno-cellulose,  24,  156 
Lime,  175 

for  causticizing,  103 
rag  boiling,  72 

mud  testing,  138 

recovery  in  soda  process,  102 


474 


INDEX 


Lime,  slaking,  175 

testing,  138 

waste,  102 

Limestone  for  acid  towers,  170 
Linen,  37 

Linings  for  sulphite  digesters,  178 
Lithography,  432 

smutting  of  ink,  440 
Loading  and  filling,  290 
Loft  drying,  260 
Logwood,  313 

M 

Machine  direction,  395 
Magazine  grinder,  213 
Manila  hemp,  39 

bleaching,  243 
Maples,  64 
Mechanical  pulp,  212 
Melt  from  sulphate  recovery,  150 
Mercaptans,  146 
Metric  and  ordinary  units  (table),  466- 

468 
Microscopic     examination     of     paper, 

386 

Milk  of  lime  acid  systems,  173 
Mineral  colors,  308,  310 
Mitscherlich  acid  tower,  169 
cooking  process,  183 
digester  lining,  179 
sizing  process,  288 
Moisture  estimation  in  lap  pulp,  371 
paper,  414 
wood  pulps,  368 
Monosulphite  of  calcium,  171,  176,  177, 

192 

Mordants,  316 
Morterud  digester,  97 
Mullen  tester,  405 
Multiple  effect  evaporation,  128 

N 

Newspaper,  fibre  from,  90 
Nitric  acid  (table),  463 
Nitro-cellulose,  13 


Ochres,  309 

Odors  from  sulphate  cooks,  142, 146, 151 

Offsetting,  437 

Opacity  of  paper,  400 

Oxide  colors,  309 

Oxycellulose,  10,  252 


Padding,  321 

Paper,  recovering  fiber  from  printed, 

Paper  mulberry,  41 

scales,  397,  398 
Paper  testing,  386 

absorbency,  410 

acidity,  422 

ash,  414 

bulk,  400 

bursting  strength,  404 

chlorine,  421 

coating,  424 

fibre  content,  387 

folding  endurance,  406 

gloss,  402 

grease-proof  qualities,  412 

groundwood  pulp,  427 

machine  direction,  395 

microscopic  examination,  386 

moisture,  414 

opacity,  400 

paraffin,  421 

permeability  to  air,  411 

physical  tests,  395 

retention  of  filler,  417 

rosin  estimation,  420 

sizing,  412,  417 

stretch,  404 

sulphur,  422 

tearing  strength,  409 

tensile  strength,  403 

thickness,  399 

unbleached  sulphite,  393,  426 

volumetric  composition,  411 

weight  per  ream,  397 

wire  side,  396 
Papyrus,  44 


INDEX 


475 


Paraffin,  determination  in  paper,  421 

Parchment  paper,  6 

Pea  vines,  44 

Pearl  hardening,  299 

Peat,  45 

Pebble  mills,  373 

Pecto-cellulose,  23 

Pectose,  93 

Perborates  in  bleaching,  249 

Permanganate  bleaching,  247,  252 

Permeability  of  paper,  411 

Permutite  water  softening  process,  358 

Peroxides  in  bleaching,  249 

Picking  of  coated  papers,  328,  439 

Pigments,  308 

Pimaric  acid,  265 

Pines,  59 

Pitch  from  waste  sulphite  liquor,  202 

Poplar,  6 1 

Porion  evaporator,  127 

Precipitated  chalk,  300 

Preston  lining,  180 

Printing,  429 

defective,  435 

inks,  434 

paper  for  different  types  of,  432 
Print-papers,  88 
Prussian  blue,  310 
Pyrites,  161,  166 

burner,  166 


Quercitron,  313 


R 


Rags,  alkali  used  in  boiling,  71 
bleaching,  240 
boilers  for,  73 
boiling,  70 
bulk  of,  65 

dusting  and  sorting,  70 
grades  of,  68 
lime  for  boiling,  72 
losses  in  treating,  76 
starch  in,  72 
washing  of  boiled,  75 


Recovery  of  sulphur  dioxide,  192 
Redwoods,  313 
Register  in  printing,  442 
Relieving  digesters,  103,  117,  189 
Resins  in  plant  cells,  35 

woods,  53 
rubber,  288 

Retention  of  fillers,  292 
Rhodamines,  319 
Rinman's   black    liquor   process,    125, 

148 
Ritter-Kellner  acid  towers,  170 

cooking  method,  184 
Rosin,  amount  used  in  paper,  271 
detection  in  paper,  419      ( 
determination  in  paper,  420 
extraction  from  stumps,  265 
in  sulphite  pulps,  195 
properties  of,  264 
recovery  from  soda  cooks,  117 
size  making,  265 
testing,  275 
Rosin  sizing,  264 

additions  to,  267 
and  hard  water,  272 
composition,  266 
defects,  274 
effect  of  sunlight,  275 
emulsifier  for,  268 
precipitation  of,  269 
troubles,  272 

Rotogravure  process,  433 
Rubber  resins  for  sizing,  288 
Rushes,  43 


SafHower,  313 

Salomon-Briingger  digester,  179 

Sand  settlers,  122 

Sapwood,  49 

Satin  white,  composition,  347 

preparation,  348 
Schopper  folding  machine,  407 

tensile  machine,  404 
Sedimentation  test,  383 
Seed  hairs,  36 


INDEX 


SSnng  (see  afeo  Roan),  tS7 
alum  used,  177 
casein,  286 
defects  of,  174 
determining  degree  of,  411 

kind  of,  417 
effect  of  drying,  173 
filkr,  271,  291 
hard  water,  353 
sunlight  on,  175 
from  sulphite  waste  liquor,  203 
glue,  187 

ink  for  testing,  413 
Mitadbertfcii  process,  *88 
reactions  in,  270 

requirements  of  different  papers,  257 
rosin,  264 
rubber  resins,  288 
silicate-starch,,  263 
starch,  262 

surface  or  tub  sizing,  258 
viscose,  287 
Smelting  furnaces,  149 
Soap  in  coating,  320,  349 

tub  suing,  259 
Soda  process,  93 

alkali  required,  "5 
black  liquor,  no,  123 
bailing  operations,  103 
caustic  soda  consumed,  112 
circulation  of  liquor,  103 
cooking  hquor  preparation,  08 

digesters,  97,  98 

discharging  digesters,  118 

effect  of  caustic  added,  107 
causticity  of  liquor,  109 
concentration  of  liquor,  106 
steam  pressure,  104 
time  underpressure,  108 

time  recovery,  102 

liquor  per  cord,  103 

loss  of  fibre.  122 

modified  forms,  115, 116 

principles  of ,  93 

rate  of  reaction,  no 

relief  of  digesters,  103, 117 


Soda  process,  rosin  recovery,  «7 

*xi.l  k>*v<.      :; 

recovery,  126 
steam  lost  on  blowing,  119 

required,  104 
sulphur  in,  115 
wash  pits,  119 
washing  black  stock,  120 
wood  preparation,  95 
woods  used,  94 

yields  from  various  woods,  114 
Soda  lost  in  process,  135 

recovery,  126 
Sodium  carbonate  (tables),  457,  458 

chloride  (table),  456 
Specific  gravity  and   Baume   (table), 
459-461 


Starch,  detection  in  paper,  418 
for  coating,  343 

sizing,  262 
modified,  344 
retention,  263 

Starch-iodide  indicator,  256 
Steam  lost  on  blowing  digesters,  119 
required  in  soda  cooks,  104 

sulphite  cooks,  185 
Steaming  wood,  220 
Straw,  41,  80 
alkali  recovery,  85 
boards,  81 
bulk  of,  66 
cellulose,  84 
chlorination  of,  86 
composition  of,  80 
cooking,  Si,  83,  86 
packing  in  boilers,  82 
retting,  86 

Stretch  of  papers,  404 
Stuffing,  321 
Sudan  m,  35 
Sulphate  process,  141 
black  hquor,  147 
by-products  from,  148 
composition  of  liquor,  144 
cooking,  143 


INDEX 


477 


Sulphate  prove**,  digester*,  142 
odors  from,  142,  146,  151 
recovered  ash,  150 
recovery  furnace*,  149 
•melting  furnaces,  149 
soda  recovery,  149 
value  of  alkalies,  143 

yield*,  145 

Sulphite  add  free  Add) 
fibre,  composition  of,  195 
proem,  156 

absorption  apparatus,  168 
cooking,  183,  191 
digesters  and  linings,  178 
modified  processes,  197 
pumping  add,  177 
reactions  of  liquor  making,  160 
storing  acid,  177 
sulphur  dioxide  preparation,  161 
theory  of,  156 
woods  for,  157,  160 
"turpentine/'  198 
waste  liquor,  198 
alcohol  from,  205 
cattle  feed  from,  203 
composition  of,  199 
destructive  distillation,  204 
fertilizer  from,  202 
fuel  from,  204 
pitch  from,  202 


tanning  materials  from, 
testing,  210 
use  as  binder,  201 
volume  obtainable,  200 
Sulphur,  161 

determination  in  paper,  422 
in  soda  cooks,  115 
per  ton  of  sulphite,  193 
sublimation,  166 
testing,  207 
use  of  molten,  162 
Sulphur  burners,  162 
air  supply,  165 
automatic  feed,  162 
color  of  flame,  166 


Sulphur  burners,  flat,  162 
rotary,  162 
temperature*  £0,165 

'•>•:.  .  ,• .  .  •.    :ft  • 

Sulphur  dioxide  (table),  446  ' 
absorption  apparatus ,  168 
ax/ting,  165, i6# 
preparation,  161 
recovery,  192 
solubiHty  in  water,  168, 446 

testing,  10$ 
Sulphur    triozide    in    burner 

165 
Sulphuric  add  (table),  465 

and  cellulose,  6 
SunBgnt,  effect  on  sizing,  27$ 
Superheated  steam  for  sulphite  ox/k- 
.-/,'<: 

'./-•••,<:'    7."      ',> 

Sycamore,  64 
Sylvic  add,  26$ 


Tables:  Aluminum  sulphate,  444,  445 
Ammonia,  4.64 

Baume*  and  specific  gravity,  450-461 
Black  liquor,  444 
Hydroduork  add,  462 
Metric  and  otdiujry  units,  4^6-46^ 
Nitric  acid,  4^3 
Physical  constants  of  the  element*. 


Sodium  carbonate,  457,  458 
Sodium  chloride,  456 
Sdphur  <fioxide  solubility,  446 
Sulphuric  acid,  465 
Temperature  com-eroons,  447 
Vapor  ptetsure  of  water,  454 
Talc,  300 

Tank  systems  for  add  making,  171 
Tanning  material  from  waste  sulphite 

Bquor,  204 

Tearing  test  for  paper,  400 
Temperature  compjiisons  (table),  447 
Tensie  ftoogik  of  paper  403 


478 


INDEX 


Testing  acid,  209 

alum,  282,  286 

black  ash  and  black  ash  waste,  140 

black  liquor,  139 

bleaching  powder,  254 

burner  gases,  208 

caseines,  339 

day,  297,  302 

colors,  322 

cooking  liquor,  137,  152,  209 

fillers,  302 

gelatine  and  glue,  261,  332 

ground  wood  pulp,  223 

lime,  138 

lime  mud,  138 

paper,  386 

rosin  and  rosin  size,  275 

soda  ash,  137 

sulphur,  207 

waste  sulphite  liquor,  210 

water,  359 

wood  pulp,  368 
Thickness  of  paper,  399 
Thiosulphuric  acid  in  sulphite  liquor, 

166 
Three  color  work,  431 

non-register,  442 
Thwing  tearing  tester,  409 
Tower  systems  of  acid  making,  169 
comparison  with  milk  of  lime  sys- 
tems, 175 

difficulties  in  operating,  171 
Tracheids,  45 
Tub  sizing  with  gelatine,  258 

starch,  262 
Tuliptree,  63 
Turmeric,  313 
Turpentine,  sulphite,  198 


U 

Ultramarine,  311 

Umber,  309 

Unbleached   sulphite   estimation,   393, 

426 
Ungerer's  cooking  process,  143 


Vapor  pressure  of  water  (table),  454 
Venetian  red,  309 
Viscose,  20,  287 

silk,  21 

Volume  composition  of  paper,  411 
Vulcanized  fibre,  colors  for,  323 

W 

Wash  pits  for  soda  fibre,  119 
Washing  black  stock,  120 

bleached  pulp,  246 

rag  stock,  75 

sulphite  fibre,  194 
Water,  351 

alum  treatment,  359 

analysis,  359 

bleach  consumed  by,  354 

classification  of,  352 

filtration,  358 

for  dyeing,  316 

iron  in,  353 

requirements  in  paper  making,   75, 

351,  353 

sampling,  360 

scale  from,  355 

soft  and  hard,  352,  364 

softening,  356 

suspended  matter  in,  354,  363 
Waterproof  coated  paper,  338,  343 
Waxes  in  coating,  329,  349 
Weight  per  ream,  397 
Weld,  313 

Willesden  products,  6 
Winestock  process  for  old  papers,  90 
Wire  side  of  paper,  396 
Witherite,  301 

Wood,  45 

barking,  158 

capacities  of  machinery  for  handling, 

160 

chipping,  159 
decay  of,  56 
fibre  length,  49 


INDEX  479 

fibres,  45  Wood  pulp  testing,  dirt  count,  383 

for  grinding,  221  loss  in  weight  on  bleaching,  382 

kinds  used,  57  moisture  determinations,  368 

moisture  in,  51  sedimentation  test,  383 

preparing,  94,  157 

proximate  analysis,  54 

requirements  for  sulphite  process,  157 

resins  in,  53  Yaryan  evaporators,  128 

weight  per  cord,  66,  114  capacities,  132 

cubic  foot,  52 
Wood  pulp  testing,  368 

beating  test,  372  Z 

bleaching  qualities,  380  Zacaton,  44 

borer  for  sampling,  369  Zaremba  evaporator,  131 

color  comparisons,  375  Zinc  chloride  and  cellulose,  5  , 


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